Why can DNA tests with mixed DNA of several people not be used to detect a criminal in a database?

Why can DNA tests with mixed DNA of several people not be used to detect a criminal in a database?

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Scenario: Two males attack another pair of two males with a weapon. The attackers are fought off and the weapon remains. Why does the police require DNA samples of the two who have been attacked to be able to find out if the two attackers are in the national criminal database?

Or without the specific scenario: Can a DNA profile be created from a sample where several individuals have been involved and it is not possible to separate the cells and assign them clearly so that this profile can then be searched for in a database?

Disclaimer: This happened to me and several years later, I'm simply curious why I had to give a sample to help police find the perpetrators.

What is genetic ancestry testing?

Genetic ancestry testing, or genetic genealogy, is a way for people interested in family history (genealogy) to go beyond what they can learn from relatives or from historical documentation. Examination of DNA variations can provide clues about where a person's ancestors might have come from and about relationships between families. Certain patterns of genetic variation are often shared among people of particular backgrounds. The more closely related two individuals, families, or populations are, the more patterns of variation they typically share.

Three types of genetic ancestry testing are commonly used for genealogy:

Variations in the Y chromosome, passed exclusively from father to son, can be used to explore ancestry in the direct male line. Y chromosome testing can only be done on males, because females do not have a Y chromosome. However, women interested in this type of genetic testing sometimes recruit a male relative to have the test done. Because the Y chromosome is passed on in the same pattern as are family names in many cultures, Y chromosome testing is often used to investigate questions such as whether two families with the same surname are related.

This type of testing identifies genetic variations in mitochondrial DNA. Although most DNA is packaged in chromosomes within the cell nucleus, cell structures called mitochondria also have a small amount of their own DNA (known as mitochondrial DNA). Both males and females have mitochondrial DNA, which is passed on from their mothers, so this type of testing can be used by either sex. It provides information about the direct female ancestral line. Mitochondrial DNA testing can be useful for genealogy because it preserves information about female ancestors that may be lost from the historical record because of the way surnames are often passed down.

These tests evaluate large numbers of variations (single nucleotide polymorphisms or SNPs) across a person’s entire genome. The results are compared with those of others who have taken the tests to provide an estimate of a person's ethnic background. For example, the pattern of SNPs might indicate that a person's ancestry is approximately 50 percent African, 25 percent European, 20 percent Asian, and 5 percent unknown. Genealogists use this type of test because Y chromosome and mitochondrial DNA test results, which represent only single ancestral lines, do not capture the overall ethnic background of an individual.

Genetic ancestry testing has a number of limitations. Test providers compare individuals' test results to different databases of previous tests, so ethnicity estimates may not be consistent from one provider to another. Also, because most human populations have migrated many times throughout their history and mixed with nearby groups, ethnicity estimates based on genetic testing may differ from an individual's expectations. In ethnic groups with a smaller range of genetic variation due to the group's size and history, most members share many SNPs, and it may be difficult to distinguish people who have a relatively recent common ancestor, such as fourth cousins, from the group as a whole.

Genetic ancestry testing is offered by several companies and organizations. Most companies provide online forums and other services to allow people who have been tested to share and discuss their results with others, which may allow them to discover previously unknown relationships. On a larger scale, combined genetic ancestry test results from many people can be used by scientists to explore the history of populations as they arose, migrated, and mixed with other groups.

How Forensic DNA Evidence Can Lead to Wrongful Convictions

Forensic DNA evidence has been a game-changer for law enforcement, but research shows it can contribute to miscarriages of justice.

Lynette White was murdered in 1988. When the three men first imprisoned for her murder were found to have been wrongfully convicted, it seemed that her killer would go unpunished. However, new technology invented in 2002 was used to analyze DNA found at the scene of the murder. The only match was to a boy too young to have committed the murder, but DNA samples were taken from his family. The youth’s uncle confessed, and was sentenced to life imprisonment in 2003.

In criminal investigation, DNA evidence can be a game-changer. But DNA is just one piece of the puzzle, rarely giving a clear “he did it” answer. According to a consortium of forensic experts who released a report earlier this year, there are limits to what DNA can tell us about a crime. And what it can and can’t reliably prove in court needs to be much clearer.

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DNA (deoxyribonucleic acid) is a code that programs how we will develop, grow, and function. Humans are thought to have DNA that is 99.9% identical, but the remaining 0.1% makes us individuals, marking us out as unique. The fact that humans and chimpanzees have just a 1% difference in their DNA further highlights how meaningful a small difference can be. Generally, the more closely related we are to someone, the more similar our DNA will be to theirs.

The tiny part of our DNA that is unique to us can be used to generate a DNA profile. This profile is usually represented as a graph showing different peaks, which reports the patterns at different points where our DNA is most likely to be unique.

An example of an STR analysis used to differentiate between DNA samples (via Wikimedia Commons)

“The increasingly prominent role played by forensic science in the administration of criminal justice is due in no small measure to the meteoric rise in DNA profiling,” wrote the law professor Liz Hefferman in a 2008 article for the British Journal of Criminology.

DNA profiling has had some remarkable successes, including finally ending a two-decade long hunt for the “Green River Killer,” who strangled at least fifty women, dumping their bodies in various spots around the Green River in Washington State. However, DNA profiles are often not clean enough to conclusively identify an individual. Ideally, a DNA sample would be complete enough to examine at least 16 different “markers,” points at which an individual’s DNA fingerprint can be sketched out. But when DNA is damaged, as it often is through exposure to moisture or extreme temperatures, only some of these markers will be available, and forensics teams will generate a partial profile. Put simply, if a DNA profile is a complete description of a person’s appearance, a partial profile might describe only one of their traits—hair color, for instance.

Partial profiles will match up with many more people than a full profile. And even full profiles may match with a person other than the culprit. Further complicating matters, a single DNA profile might be mistakenly generated when samples from multiple people are accidentally combined. It’s a messy world.

Realistically, then, DNA profiles should only be thought of as being likely to have come from a specific individual. Statistical approaches such as “match probability,” which is based on comparisons between crime scene DNA and a hypothetical “random” person, often are misunderstood. A more rigorous statistical approach is likelihood ratio, which directly compares two hypotheses: the likelihood of the DNA coming from the suspect vs. the likelihood of the DNA coming from someone else. If the likelihood ratio is less than one, the defense position (the DNA is not the suspect’s) is better supported if it is greater than one, there is more support for the prosecution case. Still, the ratio at most provides scientific support for a theory, not a yes-or-no answer.

A study from the University of California published in Law and Human Behavior tested undergraduate students’ abilities to interpret statistical evidence as it would be presented in court by prosecution and defense attorneys. The researchers found that the majority of these undergraduates failed to detect errors in statistical arguments and “made judgements based on fallacious reasoning.”

When the American Bar Association reported on DNA technology, it backed the use of DNA evidence, but urged caution in how statistics were interpreted. The ABA urged lawyers not to oversell DNA evidence and suggested that courts take the standards of the lab into account when considering DNA evidence. “Telling a jury it is implausible that anyone besides the suspect would have the same DNA test results is seldom, if ever, justified,” the report states.

In addition, the European Forensic Genetics Network of Excellence (EUROFORGEN) and the charity Sense about Science collaborated on a report released earlier this year. The report sought to clarify what DNA analysis can and cannot do within the criminal justice system. EUROFORGEN researcher Denise Sydercombe Court, based at King’s College London, said:

We all enjoy a good crime drama and although we understand the difference between fiction and reality, the distinction can often be blurred by overdramatised press reports of real cases. As a result, most people have unrealistic perceptions of the meaning of scientific evidence, especially when it comes to DNA, which can lead to miscarriages of justice.

At times, DNA evidence has been misused or misunderstood, leading to miscarriages of justice. A man with Parkinson’s disease who was unable to walk more than a few feet without assistance was convicted of a burglary based on a partial DNA profile match. His lawyer insisted on more DNA tests, which exonerated him. In 2011, Adam Scott’s DNA matched with a sperm sample taken from a rape victim in Manchester—a city Scott, who lived more than 200 miles away, had never visited. Non-DNA evidence subsequently cleared Scott. The mixup was due to a careless mistake in the lab, in which a plate used to analyze Scott’s DNA from a minor incident was accidentally reused in the rape case.

Then there’s the uncomfortable and inconvenient truth that any of us could have DNA present at a crime scene—even if we were never there. Moreover, DNA recovered at a crime scene could have been deposited there at a time other than when the crime took place. Someone could have visited beforehand or stumbled upon the scene afterward. Alternatively, their DNA could have arrived via a process called secondary transfer, where their DNA was transferred to someone else, who carried it to the scene.

Additionally, DNA technology is becoming more and more sensitive, but this is a double-edged sword. On one hand, usable DNA evidence is more likely to be detected than ever before. On the other hand, contamination DNA and DNA that arrived by secondary transfer is now more likely to be detected, confusing investigations. If legal and judicial personnel aren’t fully trained in how to interpret forensic and DNA evidence, it can result in false leads and miscarriages of justice.

Another consideration is that people shed DNA at different rates. DNA is found in bodily fluids, such as blood, semen, and saliva, but we also lose microscopic pieces of skin and hair on a regular basis. Some people lose DNA more quickly than others—if they have a skin condition, for example. If a thief uses a particular location as a stash, and a caretaker who suffers from eczema stumbles on it and reports it to the police, the forensics alone might implicate the caretaker. The quantity of their DNA present might suggest a significant period of time spent at that place. But in fact, the caretaker’s eczema resulted in more DNA being deposited there over a shorter time period.

Once a Week

National DNA databases, then, present some ethical quandaries. Many cases would never have been solved if not for DNA databases. In the Lynette White case, the breakthrough came when the police obtained the DNA profile of a relative of the murderer. However, the retention of DNA details raises legitimate privacy concerns, especially in the context of familial searching. Partial matches are more likely to lead to false positive identification of suspects who are already in the DNA database. Given that less privileged groups tend to be over-represented in DNA databases, this is a serious issue.

In 2011, a group of scientists asked whether forensic DNA databases increase racial disparities in policing. They pointed out that, in the U.S., different communities are differently policed, leading to different rates of incarceration and DNA recording. According to the study authors, actual drug use is relatively higher in white communities, but “buy and bust” operations by police are more common in African American and Latino communities, leading to disproportionate arrests.

The lesson of all this research: DNA evidence is a powerful tool in criminal investigation and prosecution, but it must be used with care. It should never be oversold in court, and it should only ever be considered in light of other available evidence. For example, if DNA is recovered in a kitchen that has been broken into, it could be from the homeowner, their guests, or even a member of the CSI team (if sufficient care hasn’t been taken to avoid contamination). If a tool-mark impression reveals that a screwdriver was used to force open the window, and DNA is recovered from a screwdriver found at the scene that does not belong to the homeowner, that’s incriminating. If that DNA is a partial or full match with an individual with the same shoe size as a footprint left in the grass under the window, even more so. If that individual has a torn piece of clothing that matches cloth fibres snagged in the window, that’s more incriminating still. If digital evidence such as their mobile phone records place them at the scene at the time the break-in happened—even though they claim to have been elsewhere—then you have a more complete picture.

Editor’s notes: An earlier version of this story contained an unclear reference to evidence seized by police investigating the murder of Meredith Kercher. The example has since been removed. We regret any error.

A study cited in an earlier version of this article is no longer available for free on JSTOR.

The Surprisingly Imperfect Science of DNA Testing

Years later, none of it — not 84-year-old Eleonora Knoernschild’s bloody body on the shag carpet, not the torn bedspread twisted around her neck, not the junk heaped on her corpse so abundantly that only her left foot poked out, not three decades of detective work — none of it would matter as much as the cheese wrapper.

The day after Knoernschild was killed on Nov. 4, 1984, the local newspapers didn’t mention the cheese wrapper at all, nor the knee-high stocking that would also be of great consequence in the trials that would take place 30 years later.

Instead, the newspapers reported how Knoernschild’s premature death had been discovered: Her daughter, 59-year-old Doris Wines, had been walking to the neighborhood donut shop that Sunday morning. Wines lived just a few doors down from her mother in St. Charles, Mo., an affluent St. Louis suburb on the western bank of the Missouri River. She stooped to pick up the newspaper on her mother’s lawn. As she went to drop it off, she saw that the window in the front door had been broken. She sprinted home and called 911.

That afternoon, police told reporters that Knoernschild had been murdered and her home ransacked. The motive was likely burglary, they said, but so far there were no witnesses or suspects.

Detective Mike Harvey of the St. Charles Police Department was assigned to the case. Harvey was a Vietnam vet with a flair for convincing criminals to rat each other out. He would devote considerable reflection over the next 30 years to the death of Eleonora Knoernschild. Long after it waned in departmental memory, he was still following leads. Even after he retired in 2009, Harvey thought about her death. So when an old friend in the county prosecutor’s office called and asked if he’d like to come out of retirement to work on cold cases for them, he did not hesitate. The Knoernschild files were the first he opened.

That was in April 2010, when the cheese wrapper had not yet gained its prominence in the case, although it had been in the custody of law enforcement for many years. Detectives found the rectangle of translucent plastic on Knoernschild’s linoleum floor next to a frozen Yankee pot roast. Over the next 27 years, the cheese wrapper sat inside a manila envelope in the St. Charles Police Department’s property room.

In November 2010, Harvey asked the county forensics lab to test it and 14 other items from the crime scene for DNA. One day the following summer, DNA technician Dan Fahnestock slid the cheese wrapper from its envelope. Fahnestock, half of the county’s two-person biological forensics lab, examined the wrapper. It was covered in silver dust, a relic of fingerprint testing it had been submitted to years before.

He wiped the wrapper with six cotton swabs and placed them each in solution to dissolve any human cells they had collected. He ran the solution through a series of machines tasked with detecting, isolating, and amplifying DNA. For each of the samples, the robots produced an electropherogram, a chart with a series of flat, squiggly lines punctuated by spikes, like the EKG of a failing heart or a seismograph recording tiny earthquakes. Several of the swabs returned nothing useful, but one produced a chart with a handful of peaks, each representing a genetic marker.

Fahnestock examined the chart. It wasn’t ideal. The amount of genetic material wasn’t exactly abundant, and the DNA had decayed considerably since 1984. Some markers couldn’t be seen at all.

Conservative technicians might have stopped there, deciding the sample was too compromised to analyze. But Fahnestock continued, piecing together a profile. That profile pointed to someone Harvey had suspected for years — St. Charles native son, Brian McBenge, an ex-boyfriend of Knoernschild’s granddaughter. Six weeks later, a DNA test of a knee-high nylon stocking found behind Knoernschild’s house implicated his younger brother, Cecil McBenge.

The DNA evidence would serve as the basis for prosecuting the brothers for first-degree murder. It was a crime Harvey believed they had gotten away with for decades. But the cheese wrapper may be evidence of something else entirely: the ambiguity of a science most people never doubt.

The man Harvey says killed Eleonora Knoernschild strode to the sturdy plastic table in the visiting room where I was seated. His goatee was sandy grey, same as his hair.

He placed a stack of papers between us: The 296-page deposition of Dan Fanhestock. In preparation for our meeting, Brian had reread the deposition, and on three sheets of yellow legal paper, in tidy print, listed dozens of page numbers where he spotted holes in Fahnestock’s DNA analyses of the cheese wrapper and stocking. He started to hand me the list, but a guard stopped him. Prisoners are forbidden from passing papers to visitors.

Brian sighed and forged ahead, flipping through the pages. He pointed to a question his attorney had asked Fahnestock: Whether Fahnestock could say with certainty that Cecil or Brian were the individuals who left the DNA on the cheese wrapper or the knee-high stocking.

Brian looked at me. “And he says no.”

Fahnestock’s answer was a simple acknowledgement that even at its best, DNA science is not absolute. To Brian, it was proof that DNA cannot be trusted.

In the three decades since DNA emerged as a forensic tool, courts have rarely been skeptical about its power. When the technique of identifying people by their genes was invented, it seemed like just the thing the justice system had always been waiting for: Bare, scientific fact that could circumvent the problems of human perception, motivation, and bias.

Other forensic sciences had taken a stab at this task. Lie detector tests, ballistics, fingerprinting, arson analysis, hair examinations — all aim to provide evidence independent of the flawed humans wrapped up in an investigation. But those methods were invented by law-enforcement agencies eager for clues it is now well established that their results are not always sound. With few alternatives, police and courts spent most of the 20th century hammering away at justice with the rubber tools of traditional forensics.

DNA was different. It came up through science, which began, in the 1950s, to unravel the ways the double helix drafts our existence. When DNA profiling led to its first conviction in a U.S. courtroom in 1987, DNA had already vaulted through the validating hoops of the scientific method. Soon it was accompanied by odds with enough zeros in front of the decimal to eliminate reasonable doubt.

Today, most of us see DNA evidence as terrifically persuasive: A 2005 Gallup poll found that 85 percent of Americans considered DNA to be either very or completely reliable. Studies by researchers at the University of Nevada, Yale, and Claremont McKenna College found that jurors rated DNA evidence 95 percent accurate and between 90 and 94 percent persuasive, depending on where the DNA was found. That faith could be shaken, but only when lawyers made a convincing case that a lab had a history of errors.

Otherwise, the mere introduction of DNA in a courtroom seemed to stymie any defense.

“A mystical aura of definitiveness often surrounds the value of DNA evidence,” the studies’ authors wrote.

In many cases, this aura is deserved. The method is unequivocal when it tests a large quantity of one person’s well-preserved genes, when it’s clear how that evidence arrived at a crime scene, and when the lab makes no errors in its work.

But those are not circumstances enjoyed by every criminal investigation. Take the case of Kerry Robinson of Georgia. Robinson was implicated, in part, when two analysts concluded his genes may be present on the victim’s vaginal swabs. The jury convicted, and Robinson received a 20-year sentence.

Greg Hampikian, a biology and criminal justice professor at Boise State University and director of the Idaho Innocence Project, was a defense expert in the trial and felt sure the analysts had reached their conclusion because of unconscious bias: They knew a great deal about the case, including that the detectives believed Robinson was guilty. To test his suspicions, Hampikian and cognitive neuroscientist Itiel Dror of University College London sent the DNA data to 17 other analysts and asked them to interpret it without any information about the case. Only one agreed with the original analysts.

Despite these results, the Georgia appeals court declined to overturn the conviction, stating that “as long as there is some competent evidence, even though contradicted … we must uphold the jury’s verdict.”

Because DNA is more reliable than other forensics, scientists have shrugged off suggestions that it could fall victim to the vagaries of bias. But Dror noted that much DNA analysis involves interpretation. With interpretation comes subjectivity, and with subjectivity can come error.

“DNA results can be in the eye of the beholder,” Dror said.

Police officer John Young was the first to arrive at Knoernschild’s house. His partner conducted a perimeter check while Young stepped over the splintered glass on the porch. The door was locked, so Young reached through its broken window and opened it. He stepped inside and found himself in the dining room.

Two cabinets and a desk had been emptied papers and pill bottles littered the floor. Kitchen cupboards were open and food cast around. Young approached a bedroom door, where a sign warned against smoking because an oxygen tank was in use. To the right, a bare mattress. To the left, a dresser emptied of its contents. On the floor, a heap of clothes and paper. He stared at it. Knoersnchild’s foot was sticking out.

He dug through the debris. Under a blue gown, he found her face. Blood ran out of her mouth and down her right cheek, forming a pool. A tube tethered her face to a nearby oxygen tank. The fringe of her bedspread encircled her neck. The coroner would conclude that blunt force trauma had killed her.

Crime-scene investigator Bob Brockmeyer arrived minutes later. He began directing a team that searched the house and neighborhood for clues. The Yankee pot roast was collected, as was the cheese wrapper. Two mismatched gloves were found in a hedge across the street their twins were in Knoernschild’s bedroom. A knee-high stocking was discovered near the garage, and another in the alley behind the neighbor’s house. One of the footprints on the front porch had a funny mesh pattern Brockmeyer hypothesized the perpetrator pulled the stocking over his boots so as not to leave footprints. These items and dozens more were placed in manila envelopes and marked as evidence.

Detective Harvey was assigned to the case that day. Over the next months, he chased leads, but nothing materialized. He would arrive at his theory that Brian had killed Knoernschild the following year, in part after realizing that Brian had once dated Knoernschild’s granddaughter, Debbie Wines.

In January 1986, Harvey interviewed Wines about her relationship with Brian. Wines had suffered a tumultuous adolescence, experimenting with booze, drugs, and boys by middle school. Her parents sent her to a series of boarding schools she’d met Brian through friends at one of them. Soon, they were dating. She introduced him to her parents, and they thought he was well mannered but didn’t like him. Something felt phony about his politeness, Don Wines would later say. Sometimes Debbie and Brian would go over to Knoernschild’s house and she would sneak $10 or $20 out of the Calumet baking powder can where her grandmother kept cash. After a while, she heard that Brian had gone out with another girl and broke up with him.

Harvey asked Wines if she was still dating Brian in early 1980, when she was 15 and he was 18, and her grandmother’s house was burglarized the first time: Cupboards were opened, junk dumped onto the floor — an uncanny preview of the crime scene four years later. Police hadn’t solved the 1980 burglary at the time, but a review of case records revealed that a fingerprint consistent with Brian’s had been lifted from the refrigerator. Wines said she couldn’t recall exactly when they broke up, so she couldn’t say if his fingerprint might have arrived there innocently. Her parents had no better recollection.

Brian’s adolescence and young adulthood were peppered with petty theft. One day, he and a friend got drunk and stole a car. Highway patrol pulled them over, and they escaped by foot. They wound up at an uncle’s house in central Missouri and continued their spree. His uncle got home and realized his truck and boots were missing, and called the police. Brian and a friend were arrested.

Like his brother, Cecil had been in and out of jail for petty crimes as a youth. One day when he was 21, he dropped some friends off at a restaurant, knowing they intended to rob it. The three were caught and arrested Cecil was convicted of attempted armed robbery and armed criminal action.

While Cecil was awaiting sentencing, Harvey came to visit him and asked what he knew about his brother’s crimes. Cecil told him that once, when his brother called from jail, Cecil asked him if he’d killed an acquaintance of theirs whose death Harvey was also investigating. Brian responded, “Is your birthday in January?” Cecil said yes. Brian replied, “Well, that’s your answer.” According to Cecil, he made up the story on a stupid, youthful whim in hopes of escaping a long sentence for the robbery charges. Harvey asked Cecil to take a lie detector test implicating his brother, but the results were inconclusive. He was sentenced to 30 years.

When Brian left prison in 1987, he married and moved to a small town in southeastern Missouri, where his wife ran a restaurant Brian was her breakfast cook when he wasn’t working construction. They raised two daughters. In 2000, Cecil was released on parole 15 years into his 30-year sentence. The following year, he was caught with cocaine at a Sammy Hagar concert and sent back. He was released again in 2003 and fell in love with an accountant named Sue. They had a daughter, adopted a dog, and bought a house.

During those years, Harvey continued investigating the brothers. He became increasingly convinced that Brian was not only responsible for Knoernschild’s death, but for two other unsolved murders from the 1980s. After joining the prosecutor’s office, he redoubled his investigative efforts, and in 2012, Brian was arrested on homicide charges in the two other cases. Harvey also led an investigation into allegations that Cecil had stabbed a fellow inmate in the early 1990s.

To Harvey’s disappointment, those cases proved to be dead ends: Brian was acquitted by a jury after 28 minutes of deliberation, and the other homicide case may not go to trial because the sole witness is now facing his own legal troubles. A judge could not find evidence that Cecil was guilty of the stabbing, and those charges were dropped. The first-degree murder charges for the death of Knoernschild, however, would prove more problematic for the McBenges.

In photos taken the morning of the murder, a police officer grasps Knoernschild’s thigh and arm, lifting her limp body to expose the blood on her bedroom carpet. In the picture, the officer is barehanded.

People familiar with his work from the 1980s say that Brockmeyer, the crime-scene investigator, and his team probably weren’t wearing masks the day they searched Knoernschild’s house for clues, and likely used brushes and equipment that was not often cleaned between crime scenes (Brockmeyer died of a heart attack in 2003). The following day, Brockmeyer checked the stocking into the St. Charles Police Department’s property room, but he waited to turn over the cheese wrapper and several other items for nine days. He may have held onto them to do his own fingerprint processing, but it’s unclear — there is no record of the cheese wrapper’s whereabouts during that time.

The stocking was eventually sent to Southeast Missouri University (SEMO) in Cape Girardeau, where Professor Robert Briner trained graduate students in forensic analysis in a house-turned-lab. According to his records, he tested the stocking for saliva secretions, and found none. Enough time has passed that he does not remember specifically if he used a mask, or what evidence from other cases were tested in the same workspace, or which graduate students may have been around during testing.

Several months later, the stocking was sent back to St. Charles, where it joined the cheese wrapper in the evidence room. They sat there for more than two decades, until they were sent to Fahnestock for DNA testing. The cheese wrapper arrived at the crime lab in a sealed envelope the stocking in an unsealed one.

As Fahnestock handled the evidence, he wore two layers of gloves, a facemask, and the evidence only touched surfaces that were covered with clean sheets of butcher paper. Despite these precautions, Fahnestock found his DNA on an item from Knoernschild’s house: A sample he tested from a blue glove discovered at the crime scene included at least two DNA profiles, one of which appeared to be his own.

Scientists are still exploring the circumstances and ease with which DNA can travel. Many of our cells and fluids — skin, saliva, sweat, and mucus — routinely find their way into our environment. If conditions are favorable, our genes can wind up places we’ve never been. After Silicon Valley millionaire Raveesh Kumra was killed in his 7,000-foot mansion in November 2012, police discovered the DNA of Lukis Anderson, a 26-year-old homeless man, on his fingernails. But hospital records indicated that Anderson was unconscious in a hospital bed while Kumra asphyxiated nine miles away.

Anderson spent five months in jail while lawyers and investigators pondered how he could have committed the crime. Finally, they realized that the paramedics who transported Anderson to the hospital had also responded to the homicide. They had clipped an oxygen-monitoring probe to Anderson’s finger that morning, and to Kumra’s that afternoon. Anderson’s DNA had gone along for the ride.

“It’s a small world,” Santa Clara County Deputy District Attorney Kevin Smith told the San Francisco Chronicle after the mistake was discovered.

Peter Gill is a giant in the forensic DNA community, counted among the scientists who wrote the original paper conceptualizing DNA as a forensic tool in 1985. But he has spent recent years warning people using his tool against blindly trusting its results. In a 2014 book called “Misleading DNA Evidence: Reasons for Miscarriages of Justice,” Gill wrote that contamination is dangerous because investigators are eager to believe that DNA found at a crime scene must come from the perpetrator.

“The presence of a DNA profile says nothing about the time frame or the circumstances under which it came to be there,” says defense expert and researcher Dan Krane. “Test results can’t distinguish between the possibility of contamination, or evidence tampering, or, you know, murder.”

Technology may soon increase the danger of implicating innocent people. Today, most DNA analytical machines are optimized to parse the DNA of about 100 human cells. Future generations of forensic robots may extract a profile from just one. The DNA of a person who drives by a crime scene with an open window could wind up somewhere suspicious shake someone’s hand before he commits a crime, and you may be implicated.

“Next gen sequencing might generate lots of data from small amounts of DNA, but you’re still faced with the same fundamental question — what does it mean?” said John Butler, special assistant to the director for forensic science at the National Institute of Standards and Technology, who has written several textbooks on DNA analysis. “You could detect a single cell on a knife blade, but that doesn’t mean anything — it might have arrived there long before the crime or been transferred there by chance.”

Everyone on the McBenge brothers’ defense team has a theory about how Cecil and Brian’s DNA could have found its way onto the evidence some are more far-fetched than others. Cecil’s attorney Cyndy Short wondered if Knoernschild had tossed the stockings out by the trash cans days before she died, and Cecil, who lived a mile away, walked down the alley and sneezed. Bicka Barlow, another attorney and DNA expert on Cecil’s defense team, noted that a refrigerator repairman had visited the house earlier that week — perhaps a cheese wrapper that Brian had touched when he was dating Debbie had been sitting behind the fridge for years before it was somehow loosened onto the crime-scene floor. DNA expert Dan Krane of Wright State University in Dayton, Ohio, who testified for the defense, speculated that the investigators’ fingerprint brushes could have transferred Brian’s DNA onto the wrapper. “It doesn’t matter how long before the crime [Brian] was in the house, all that matters is that he was,” Krane said.

Eighteen pieces of evidence were tested from the crime scene, including knives found in the bedroom, the ligature around her neck, and the nightgown she was wearing while she was killed. Had the McBenges’ DNA appeared on anything intimate to the crime, the defense believes there would be less to speculate about. “But it was on a damn cheese wrapper,” said Short. And a cheese wrapper, she said, doesn’t tell the story of a murder.

The nylon stocking found in the back alley was even farther from the crime scene. Investigators have toyed with how it may have been deployed: First, they theorized it was pulled over a boot. Later, they speculated it was worn as a glove or a mask.

Prosecutor Phil Groenweghe said he doesn’t need to know exactly how it was used. “There are limits on what we can say happened because the only eyewitness is dead,” he said. “In a criminal prosecution, there’s certain elements that have to be proven, and the point in time when they put on the nylons isn’t one of them.”

Groenweghe disputed that the DNA could have arrived on the cheese wrapper or stocking innocently. “DNA was found on items that clearly had been touched at the time of the crime. We didn’t find it on the door jam.”

He also dismissed any theory that placed the DNA on the two items by accident. “Unless Brian and Cecil were working as lab techs at SEMO, I don’t think that’s a very compelling defense,” he told me. “The fact is, it was their DNA on the evidence.”

But the McBenges challenge whether it was their DNA at all.

In the three years between the McBenges’ arrest and their trial, Fahnestock worked hard to make sure that the DNA he’d found didn’t belong to any of the bare-handed people who had handled the evidence. He tested the DNA samples of half a dozen current and retired police officers. He tested Dr. Robert Briner of SEMO. He tested everyone in Knoernschild’s family. He tested Debbie’s live-in boyfriend from 1984. He tested the cleaning lady who had waxed Knoernschild’s floors. He even tested Brockmeyer, who had passed away years earlier, by testing his son and wife.

As Fahnestock has explained to dozens of juries, crime labs don’t exactly map the human genome. Instead, they typically focus on 13 places, or loci, plus a 14th that expresses gender. Each loci is home to two alleles, one inherited from each parent. On an electropherogram, these alleles show up as spikes, and vary from person to person. We usually share half or more of our markers with close relatives, and often share several with complete strangers. But by the FBI’s statistics, the probability of sharing all 13 loci with someone you’re not related to is lower than 1 in a trillion.

The cheese wrapper had only produced a partial profile spikes showed up at just six of 13 loci. This didn’t surprise Fahnestock. As DNA ages, it breaks down. Some markers are famous for crumbling into illegibility right away others can be detected decades later. All things considered, six loci seemed reasonable for a sample from the 1980s.

But the partial profile put Fahnestock in a quandary. At the time, he didn’t know whose DNA he had found, so he wanted to search the federal database for the profile. That database, called the Combined DNA Index System, or CODIS, contains more than 14 million profiles, including all convicts and many arrestees from the state of Missouri for the last 15 years. But it cannot be searched without entering at least ten of the 13 loci, and Fahnestock only had six. Fahnestock asked for permission to make an exception and search for the partial profile — an uncommon but not unheard of request. After some discussion and paperwork, the state database administrator agreed.

When Fahnestock ran the cheese wrapper through the database, it returned 10 candidates — all ten were technically “matches” for the profile found on the cheese wrapper. Though we think of a DNA match as unambiguous, partial profiles have so little genetic material that they can result in several potential matches, and analysts must interpret which match looks best. Fahnestock did just that and then disregarded the nine other matches.

A few days later, he learned the identity of that match: Brian McBenge.

The defense team argued that because the profile was incomplete, it was more likely to be a false positive — a hit by unhappy happenstance.

It’s not clear how often coincidental matches occur. The FBI has argued that it’s rare, but some statisticians disagree, as a 2008 investigation by the Los Angeles Times revealed. The newspaper wrote that a rogue Arizona state employee had run tests on the state’s database without the FBI’s permission and found 122 pairs of profiles that matched at nine or more loci. Twenty of them matched at 10 loci. One pair matched at 11 and another at 12. This all happened in a database with just 65,493 profiles.

The Arizona results were not anomalous: In Illinois’s database of 220,000 profiles, a search found 903 pairs that matched at nine or more loci. Bureau experts say some matches can be expected in a large database, and that others may be close relatives or accidental duplicates. But they have halted further investigation of their statistics, citing privacy concerns.

Database matches are tricky. They can sometimes solve otherwise inscrutable cases, but they can also lead investigators down the wrong path. In one case in Bolton, England, police deduced a six-loci profile from blood discovered on the window of a burglarized home. The trouble was, the DNA matched a man with advanced Parkinson’s disease who could barely walk. But the match statistic — 1 in 37 million — seemed so definitive that police arrested him anyway. He was finally vindicated after more advanced DNA tests revealed that he shared a partial profile with the culprit.

When a suspect has been discovered because of a database match, courts must decide how much weight to give that evidence, and different statistical methods can arrive at wildly different results. The method used by Fahnestock calculates how often the profile is expected to occur randomly in the population. After his initial tests, he calculated that the probability of a random person having the profile he found on the cheese wrapper was 1 in 741,000 among Caucasians.

Defense expert Dan Krane came up with a different statistic: 1 in 2.5.

The reason for the yawning difference, Krane explained, is that his method takes into account the likelihood of a coincidental match in a specific database. For instance, if you search a database of 1 million for a profile that 1 in 100,000 people share, you would expect around 10 hits. If you arrested any of them without other evidence, you’d probably get the wrong person. The method was endorsed by a special advisory group to the FBI and a National Research Council panel, but is sometimes withheld from court in an attempt not to confuse jurors with statistical arguments.

The McBenge team contends that because the DNA on the cheese wrapper was degraded, it was far more likely to produce a false positive than a full profile would have. If investigators had found substantial other evidence pointing to their guilt, the database hit, even one with a 1 in 2.5 chance of being reliable, would have been the cherry on top. But without that substantial evidence, the juries were left to decide how much faith to place in the DNA.

In contrast to the minimal spikes on the cheese wrapper’s electropherogram, the stocking’s chart was a mountain range. There could be only one explanation: Genes from multiple people were on the nylon. One of those people appeared to be Knoernschild, which was a good sign for the prosecution’s theory. The stocking, though found in the back alley, had probably come from her house.

Identifying who else was on the stocking was more challenging — particularly because the DNA there was degraded, so only some markers could be detected. Fahnestock approached the problem by puzzling out the spikes that didn’t belong to Knoernschild and creating a theoretical profile of a second contributor. Because that profile had at least one matching gene at 10 loci, Fahnestock didn’t need special permission to run it through the federal database. The result matched Cecil McBenge.

In forensic science, interpretation of mixtures is a known danger zone. When a sample has more than one person’s DNA, as the stocking did, the analyst must interpret the data, making decisions about how many individuals may be in the mix, and which spikes belong to which person. When people in the sample happen to have similar genes, it gets more complicated. Cecil and Knoernschild shared alleles at seven of their 13 loci.

A 2013 survey by the National Institute of Standards and Technology asked analysts from 108 labs to look at a three-person mixture and determine if a suspect’s DNA was present. Seventy percent of the analysts said the suspect might be in the mix 24 percent said the data was inconclusive. Just six percent arrived at the truth: The suspect was not in the sample.

Not only do analysts vary in their interpretation of evidence, they also disagree over how certain to feel about the results. In another NIST survey, labs interpreting a two-person mixture came back with match probabilities that varied by 10 orders of magnitude. “Imagine if you take a pregnancy test and you send it to two different labs,” said Greg Hampikian, who authored the study on bias in the Atlanta rapist case, “and one said the odds are a billion to one that you’re pregnant, and the other said it’s 50-50.”

Because different analysts can reach different conclusions about the same DNA evidence, savvy investigators shop evidence around to get the results they want. In one instance, the California Innocence Project had a large private lab test evidence attorneys believed could exonerate a convicted murderer in Los Angeles. That lab reported the DNA was inconclusive. So lawyers took the same data to another analyst. By her assessment, the evidence plainly cleared the convict.

California Innocence Project attorney Mike Semanchik said he had no qualms about asking multiple analysts to look at the same data — doing otherwise would be a disservice to his client. Nonetheless, the implications are troubling, he said. “How can two labs get entirely different answers from the same DNA tests?”

Even the most automated part of the process — the analysis performed by machines — varies from lab to lab. Among other tasks, forensic profiling equipment amplifies DNA to an observable level. Most labs amplify DNA to the maximum the manufacturer recommends. But when that isn’t enough to produce legible spikes, some labs will hike up amplification or otherwise futz with the settings to get results.

Methods that push equipment beyond its normal bounds are commonly called low copy number DNA testing, or LCN testing. This is the most controversial practice in forensic biology today because of the errors it can produce. Pushed too far, the results will begin to show spikes where there are none, while other spikes disappear.

In New York City, the Office of Chief Medical Examiner has embraced LCN it is the only public forensics lab in the country to have done so. Lab officials say they only use the technology in ways that are scientifically valid and reliable, and the New York State Commission on Forensic Science sanctioned the method in a series of contentious votes.

Last fall, commission member Barry Scheck voiced his concern about the method at a hearing of the DNA subcommittee. Before Scheck made his name disputing DNA as O.J. Simpson’s lawyer, he founded the Innocence Project, which has used DNA to exonerate hundreds of wrongfully convicted people. He said he opposes the use of cutting-edge DNA forensics in court because he doesn’t think they have been sufficiently proven. Scheck had been demanding the Office of Chief Medical Examiner make public its internal validation studies on LCN, which it has refused to do. At one point, after an otherwise subdued hearing, he yelled to some of the subcommittee members: “YOU ARE ALL FUCKING LYING!”

San Francisco resident Gale Joseph Young spent years incarcerated while lawyers fought over LCN testing. Young had been questioned and strip-searched in a San Francisco police station on suspicion of selling drugs in 2008. Officers found nothing on him, but after releasing him, they saw a plastic baggie with 14 grams of crack cocaine on the floor. There was so little DNA on the bag that the crime lab used LCN to get results, and concluded that he might be in the mix.

Despite defense objections, these results were allowed in court. One jury hung a second convicted. The case was appealed to U.S. District Judge Maxine Chesney, who was tasked with deciding the LCN question. Chesney, befuddled by the technical arguments, ruled the LCN evidence was admissible because neither side was “being ridiculous in their general approach.” The case was appealed to the Ninth Circuit Court, which reversed her decision and admonished her for failing to adequately evaluate the science (“Not being ridiculous is not synonymous with being reliable.”)

Unfortunately for the clarity around LCN, neither Chesney nor the higher court ruled on the validity of the science itself, because by then, Young had already served a five-year, 10-month sentence, and prosecutors dropped the charges.

Fanhestock says his lab avoids such controversy by staying away from LCN testing altogether. If a sample has less DNA than his equipment has been validated for, he won’t blow it up with more amplifications.

But defense attorney and DNA expert Bicka Barlow countered in depositions and in court that his lab did toy with LCN in the McBenge cases: She noted that in some tests, he had doubled the quantity of DNA and increased testing time in order to heighten the low spikes. These techniques, she said, could result in errors. Fahnestock maintained that his methods were valid and uncontroversial and his results were reproducible.

To see if they were, seven analysts agreed to participate in an informal experiment for this story. This experiment, though hardly randomized or double-blind, would hopefully yield insights about the precision of DNA forensics. The participants studied the original electropherograms and accompanying data from the cheese wrapper and stocking in Knoernschild’s case, and deduced the DNA profiles on them. When the results came back, Dr. Lawrence Kobilinsky, chair of forensic science at John Jay College of Criminal Justice in New York, scrutinized them for variance. It wasn’t hard to find. Two of the seven respondents wouldn’t do the analysis as directed, because they were instructed to go about it exactly as Fahnestock had — without a stochastic threshold.

A stochastic threshold is a way to anticipate problems: The threshold is established by testing equipment with shrinking amounts of DNA until the results are no longer accurate. Anything below the threshold is unreliable. As of 2012, about 86 percent of labs used a stochastic threshold. But in 2011, Fahnestock was still using equipment for which a stochastic threshold had never been established. (In 2014, Fahnestock retested a different patch of the stocking on newer equipment that did have a stochastic threshold, but he couldn’t do the same for the cheese wrapper, because all the DNA had been used in the initial testing.)

Even those analysts who participated arrived at different results, particularly in their certainty statistics. For the cheese wrapper, Fahnestock had ascribed a probability of 1 in 741,000 of a random match. The seven analysts’ rates spread from 1 in 3,670 to 1 in 593,000 (a full profile would have resulted in a statistic closer to 1 in 1,000,000,000,000,000).

The stocking provided even less consensus. Fahnestock had assumed a mixture of two people — Cecil and Knoernschild. One analyst concluded it was a mix of at least three. Another came up with a result that excluded Cecil entirely.

Again, the certainty rate was wholly uncertain. Fahnestock’s final analysis ascribed a probability of 1 in 6.17 million of a random match the analysts’ stats ranged from 1 in 4,470 to 1 in 106 billion. “I’m kind of astonished that there would be that much variation,” Kobilinsky said. “They all have the same job, and they’re coming up with different results.”

The trial of Brian McBenge began in August 2014 his brother’s trial began six weeks later.

They were each charged with first-degree murder, so the prosecution had to prove they’d killed with intent. Prosecutors maintained that Brian had burglarized Knoernschild’s house in 1980, and returned four years later with his brother in search of more loot. This time, prosecutors said, Knoernschild was at home, so they killed her.

Brian was neither questioned nor charged at the time of the 1980 burglary. But Debbie Wines testified that she now remembered breaking up with Brian before that burglary, so there would be no legitimate reason for his fingerprint to be on the refrigerator. The prosecution showed the jury side-by-side photographs of the 1980 and 1984 ransackings. The same cupboards were opened, food dumped on the floor. Brian had motive and opportunity in both instances, the prosecutors told jurors, because he knew about the cash-filled Calumet can.

The defense teams attacked this evidence the fingerprint was only partial, and Debbie’s memory of when she and Brian broke up was hazy at best, they said. The crimes had happened so long ago that neither Cecil nor Brian could provide an alibi. And there was no evidence that anything had been stolen from the house in either burglary: In 1980, Knoernschild hadn’t reported any money missing in 1984, the can was found apparently untouched in the back of Knoernschild’s closet. Money was also found in her purse.

But neither a fingerprint nor a can of cash were likely to return a verdict. The outcome depended on the DNA found on the cheese wrapper and stocking. For a conviction, the jury would have to trust the DNA. For an acquittal, the jury would have to believe that DNA forensics can arrive at the wrong answer.

The prosecution blew up the electropherograms to poster-size and explained each spike to the jury. The defense attacked the relevance of those spikes: The DNA was found on items not intimate to the crime. Fifteen fingerprints were lifted from her house after she was killed — none were traced to Cecil or Brian. If they had committed the crime, Cecil’s attorney Cyndy Short said, how could they leave so little of themselves behind?

The prosecution countered. How likely was it that two brothers’ DNA could accidentally arrive on two pieces of evidence from the same crime scene?

The defense walked the jury through statistical and technical arguments to describe how that may have happened. The DNA was degraded, mixed, contaminated, meager and partial — a complete catalog of the danger zones in DNA analysis. The gap between good science and infallible science is wide, Short argued, and left ample room for reasonable doubt.

The totality of the state’s evidence against Cecil and Brian, Short concluded, was one partial fingerprint from the 1980 burglary, the photos comparing the crime scenes from 1980 and 1984, and DNA on a cheese wrapper and a knee-high stocking.

The jury took four hours to convict Brian McBenge. He received a life sentence. A month and a half later, another jury delivered the same verdict to Cecil.

The judge in Cecil’s trial, Daniel Pelikan, could not comment on the specifics of the case, but said his juries have typically found DNA evidence extremely persuasive. “In all my cases, I warn the juries that the trials take longer than an hour to complete, and not every case has fingerprints, saliva, semen, and DNA,” he said.

But, Pelikan added, “We have a well-educated, sophisticated jury pool in my county. I’ve always been impressed with their ability to understand the science.”

The McBenges are now appealing their convictions on more than a dozen points. Cyndy Short is optimistic about the chain of custody question: That the cheese wrapper wasn’t checked into evidence for nine days after Bob Brockmeyer collected it, for instance, and the stocking arrived to the crime lab for testing in an unsealed envelope. The defense team is less hopeful about their appeal on the strength of the evidence DNA evidence does not tend to inspire doubt.

Mixture Interpretation: Why is it Sometimes So Hard?

A DNA profile from such a scenario is shown in Figure 1. Here there are no more than four alleles at any locus, and peak height ratios are consistent with only two sources at all loci (e.g., fairly balanced and uniform peak height ratios at loci with four alleles and altered peak height ratios consistent with shared alleles at all loci with two or three alleles). It is thus reasonable to assume that there are only two sources of DNA in this profile. DNA analysts can interpret these data and calculate statistical frequencies with great confidence.

Figure 1. A 1:1 mixture of DNA from two sources.

0.5ng of total DNA from a 1:1 mixture of DNA from two sources was amplified with the Promega PowerPlex® 16 HS System. One microliter of amplified product in 10µl of Hi-Di™ formamide/ILS was injected on an Applied Biosystems 3130xl Genetic Analyzer, and the data were analyzed using GeneMapper® ID-X. All alleles from both sources are present.

As the difference in the amount of the DNA contributed by the two sources increases, there becomes a point at which a clear major profile emerges that for all purposes can be treated as a single-source profile for interpretation and statistical calculations—the simplest scenario (Figure 2). Under this situation, the minor contributor’s profile also may be complete and easily interpreted (with the possible exception of shared alleles) or may be incomplete and more difficult to interpret as the disparity in the amounts of DNA from the two sources increases and alleles drop below the analytical and/or stochastic thresholds.

Figure 2. A 9:1 mixture of DNA from two sources.

0.5ng of total DNA from a 9:1 mixture of DNA from the same two sources as in Figure 1 were amplified with the Promega PowerPlex® 16 HS System and processed as in Figure 1. All alleles from both the major DNA source and minor DNA source are present.

In many cases, minor alterations in one or more of the parameters listed in the first paragraph may have a minimal effect on the ability to confidently interpret a mixed DNA profile, especially if the amount of each DNA amplified is sufficient. Some three-person mixtures can be fairly easy to interpret, particularly if the individuals are unrelated and have few alleles in common and there are two “major” sources. Interpretation becomes even simpler if one of the sources is known (e.g., fluid and/or cells, fingernail or swab taken from an individual) and the profile from that individual can be removed easily, leaving two decipherable profiles. Limited degradation that only affects one or a few of the loci with the longest DNA sequences may have little effect on interpretation, particularly if the data from those loci can be recovered by a second amplification with more of the same DNA or by using mini-STRs. A single stutter peak or artifact generally has no impact on interpretation of the DNA profile(s) from the major source(s). On the other hand, significant alterations to any of the parameters listed (e.g., increasing the relatedness or number of alleles shared among the sources, increasing the number of contributors and/or the disparity in the amount of DNA from each source, an increase in the amount of degradation and/or presence of artifacts) will likely make mixture interpretation more complex a combination of several alterations generally confounds the interpretation significantly.

The most problematic scenario for mixture interpretation, however, is when the amount of DNA amplified is limiting for one or more of the sources in a mixture. Interpretation of the DNA profile from the limited source(s) can become difficult to impossible due to the inability to confidently detect stochastic effects that may be present. Stochastic effects can result in any of the following observations in the mixed DNA profile:

  1. extreme peak height imbalance due to the unequal presence and/or amplification of alleles from each source. This imbalance, which may be compounded by variation in pipetting and/or electrokinetic injection, appreciably affects one’s ability to calculate an accurate ratio of DNAs in the mixture. As a result, it becomes difficult to correctly associate alleles [and thereby “restrict” genotypes (1)] for individuals within a locus or across loci in a profile, especially since the number of sources that contributed to the mixed DNA sample is unknown. Even samples amplified with sufficient amounts of DNA show some normal variation in peak heights (see Figure 3).
  2. the loss of some alleles (the extreme case of peak height “imbalance”) for one or more sources at a locus (termed “allele drop-out”) or the loss of all alleles at a locus (termed “locus drop-out”) due to the small amount of DNA present. The uncertainty regarding whether a complete or partial DNA profile is present may affect the ability to: a) determine if the source(s) of DNA are homozygous or heterozygous at a locus b) associate genotypes across loci and c) accurately estimate the minimum number of DNA sources in the mixture.
  3. the presence of additional peaks labeled as alleles that are not from the original sources (termed “drop-in”). These peaks may be due to several different possibilities (e.g., increased stutter peak height due to the production of stutter peak products in early amplification cycles, other random artifacts of amplification, electrophoresis, detection and/or analysis that cannot be distinguished from true alleles, or low levels of sporadic contamination of one or a few DNA templates or products introduced anywhere in the process), and can lead to overestimation of the minimum number of sources to the DNA profile and the possible risk of false-inclusion of an individual.

Figure 3. Peak height imbalance.

Three replicate aliquots of 1ng of a single-source DNA from a combined DNA plus master mix solution was amplified with the Applied Biosystems Identifiler® kit. One microliter was injected for 2 seconds on an Applied Biosystems 3130 Genetic Analyzer, and the data were analyzed using GeneMapper® ID-X. All variation in peak heights and peak height imbalance is due to variability in amplification, pipetting and electrokinetic injection.

From the data alone, it is reasonable to assume that the profile in Figure 1 does not suffer any stochastic effects and thus contains all alleles from the contributing sources based on the peak heights present. If all alleles from a known individual are present in this mixture, then that individual is included as a possible source. In contrast, the absence in this mixture of one allele (and certainly more) that is present in the profile from a known individual warrants excluding the individual as a source. However, the minor source of DNA in Figure 2 has some alleles with lower peak heights that may be near or below the stochastic threshold, introducing some possibility that the profile may be incomplete. In addition, some unlabeled stutter peaks at similar heights to the detected minor alleles also may need to be considered in the interpretation and statistical calculations. Restricting genotypes for a single minor contributor is simple at a few loci (e.g., TH01, Penta E) but more complex at others (e.g., D18S51, D16S539) restricting genotypes if there were two minor sources of DNA would be impossible.

Where it is difficult to reasonably assume the number of contributors due to shared alleles and/or limiting amounts of DNA with associated stochastic effects, it is important to consider the profile under different assumptions when the comparison is made to a known individual’s profile. Caution should be used in declaring that a major source profile is present, as the highest peaks may simply represent the additive effect of alleles shared by two or more of the sources. It may be necessary to report the conclusions using different assumptions (e.g., mixture of two sources vs. mixture of three sources). This is especially true if the conclusions for an individual being compared to the evidence profile change under the different assumptions (e.g., excluded if two sources vs. included or inconclusive if three or more sources of DNA).

Due to the complications inherent in interpretation of partial and/or complex mixed DNA profiles, it is imperative that all profiles are thoroughly assessed and that the alleles relied on for interpretation and calculation for statistical frequencies be recorded prior to any comparison to profiles from known individuals. It might be helpful to record (e.g., on a worksheet) any decisions made during the assessment of the profile for reference at a later time (e.g., discussions with technical reviewer, technical leader or attorney(s), or during testimony) and establish the assumptions that may be used during interpretation and reporting. Similarly, determinations that a profile is unsuitable for interpretation and comparison should be made prior to referencing any known profiles. These steps will help ensure that no bias is introduced during the final interpretation process.

The DNA tests that we routinely use in our laboratories are designed to be exclusionary tests. That is, testing is performed under the premise that an individual who is not the source of the DNA with a single-source profile or who is not one of the sources in a mixture of DNA is expected to be excluded from the DNA sample. This premise holds true when a complete multi-locus single-source profile is obtained. However, as the number of sources in a mixture increases along with the concomitant increase in the number of alleles to interpret, and as the relatedness of a non-source to a true source increases, the ability to exclude a falsely accused individual decreases. The statement of “inclusion” under these scenarios may have little meaning, and the frequency of the mixed DNA profile results may be quite common. “Inconclusive” or “insufficient for comparison purposes” may be the more appropriate conclusion in some cases.

Similarly, as the quality of a DNA profile decreases (e.g., partial profile) the number of loci available for interpretation also decreases with the concomitant increase in the number of inconclusive loci, and again, the ability to exclude a falsely accused individual decreases. Fortunately, the statistical significance of the inclusion decreases proportionally however, caution should always be used to ensure that strict guidelines for inclusion vs. exclusion (and inconclusive) are followed. Statements of inclusion and exclusion have powerful ramifications in our justice system. Care must be taken to provide all parties (e.g., law enforcement, attorneys for both sides and the judge and jury if the evidence makes it to court) a clear understanding of the limitations of a multiple-source mixture and the meaning of an inclusion or an exclusion for a particular sample in the context of the case. This is especially important when the “match” is a partial inclusion of a partial profile with statistical frequencies that are not rare. The term “cannot be excluded” really means the same as “included” these statements are synonymous conclusions, and thus, always should be followed by appropriate statistical calculations. When there is a temptation to report “cannot be excluded” instead of reporting that an individual is “included as a (possible) source”, be aware that there is some likelihood that a bias against exclusion or inconclusive and pro-inclusion may be favored. In some cases, either of these statements of non-exclusion can be compelling (and possibly misinterpreted as statements of identification of the source) regardless of the associated statistical frequencies.

For samples where there is an uncertainty regarding the number of DNA sources and whether the profile is partial or complete, mixture interpretation can be difficult and analysts may have differing opinions on how to interpret the data. In this situation, amplifying more DNA and/or extracting DNA from other regions of the item or from separate items in the case may prove beneficial.

There is an extensive list of publications relevant to DNA mixture interpretation in forensic cases (1,2). These studies may be used by forensic laboratories in conjunction with well-designed and carefully reviewed internal validation studies to establish effective standard procedures for DNA-testing parameters and their appropriate associated mixture-interpretation policies. Sensitivity studies and mixture studies covering all ranges of DNA tested under all parameters in the laboratory can provide a strong foundation to the laboratory for assessing the range of peak height ratios and stutter percentages routinely observed in the laboratory and for establishing appropriate analytical and stochastic thresholds for data analysis along with rigorous guidelines for consistent profile interpretation and statistical frequency calculations. Casework profile data using samples from known individuals may be used to enhance the established procedures by providing valuable perspectives on the limitations and parameters of DNA mixture interpretations. These measures, used in tandem with a comprehensive analyst training program, help ensure interpretation and reporting consistency throughout a laboratory. This is turn results in neutral, reproducible and accurate interpretation of the available DNA profile data.


Thank you to Martin Ensenberger of Promega Corporation and to Dr. Robin Cotton of Boston University for generously providing the profiles for the figures, and to Todd Bille, John Butler, Mike Coble, Robin Cotton and Catherine Grgicak for very helpful discussions on mixture interpretation.


The past decade has seen great advances in a powerful criminal justice tool: deoxyribonucleic acid, or DNA. DNA can be used to identify criminals with incredible accuracy when biological evidence exists. By the same token, DNA can be used to clear suspects and exonerate persons mistakenly accused or convicted of crimes. In all, DNA technology is increasingly vital to ensuring accuracy and fairness in the criminal justice system.

News stories extolling the successful use of DNA to solve crimes abound. For example, in 1999, New York authorities linked a man through DNA evidence to at least 22 sexual assaults and robberies that had terrorized the city. In 2002, authorities in Philadelphia, Pennsylvania, and Fort Collins, Colorado, used DNA evidence to link and solve a series of crimes (rapes and a murder) perpetrated by the same individual. In the 2001 “Green River” killings, DNA evidence provided a major breakthrough in a series of crimes that had remained unsolved for years despite a large law enforcement task force and a $15 million investigation.

DNA is generally used to solve crimes in one of two ways. In cases where a suspect is identified, a sample of that person’s DNA can be compared to evidence from the crime scene. The results of this comparison may help establish whether the suspect committed the crime. In cases where a suspect has not yet been identified, biological evidence from the crime scene can be analyzed and compared to offender profiles in DNA databases to help identify the perpetrator. Crime scene evidence can also be linked to other crime scenes through the use of DNA databases.

For example, assume that a man was convicted of sexual assault. At the time of his conviction, he was required to provide a sample of his DNA, and the resulting DNA profile was entered into a DNA database. Several years later, another sexual assault was committed. A Sexual Assault Nurse Examiner worked with the victim and was able to obtain biological evidence from the rape. This evidence was analyzed, the resulting profile was run against a DNA database, and a match was made to the man’s DNA profile. He was apprehended, tried, and sentenced for his second crime. In this hypothetical case, he was also prevented from committing other crimes during the period of his incarceration.

DNA evidence is generally linked to DNA offender profiles through DNA databases. In the late 1980s, the federal government laid the groundwork for a system of national, state, and local DNA databases for the storage and exchange of DNA profiles. This system, called the Combined DNA Index System (CODIS), maintains DNA profiles obtained under the federal, state, and local systems in a set of databases that are available to law enforcement agencies across the country for law enforcement purposes. CODIS can compare crime scene evidence to a database of DNA profiles obtained from convicted offenders. CODIS can also link DNA evidence obtained from different crime scenes, thereby identifying serial criminals.

In order to take advantage of the investigative potential of CODIS, in the late 1980s and early 1990s, states began passing laws requiring offenders convicted of certain offenses to provide DNA samples. Currently all 50 states and the federal government have laws requiring that DNA samples be collected from some categories of offenders.

When used to its full potential, DNA evidence will help solve and may even prevent some of the Nation’s most serious violent crimes. However, the current federal and state DNA collection and analysis system needs improvement:

(1) In many instances, public crime labs are overwhelmed by backlogs of unanalyzed DNA samples.
(2) In addition, these labs may be ill-equipped to handle the increasing influx of DNA samples and evidence. The problems of backlogs and lack of up-to-date technology result in significant delays in the administration of justice.
(3) More research is needed to develop faster methods for analyzing DNA evidence.
(4) Professionals working in the criminal justice system need additional training and assistance in order to ensure the optimal use of DNA evidence to solve crimes and assist victims.

President Bush believes we must do more to realize the full potential of DNA technology to solve crime and protect the innocent. Under the President’s initiative, the Attorney General will improve the use of DNA in the criminal justice system by providing funds and assistance to ensure that this technology reaches its full potential to solve crimes.

One of the biggest problems facing the criminal justice system today is the substantial backlog of unanalyzed DNA samples and biological evidence from crime scenes, especially in sexual assault and murder cases. Too often, crime scene samples wait unanalyzed in police or crime lab storage facilities. Timely analysis of these samples and placement into DNA databases can avert tragic results. For example, in 1995, the Florida Department of Law Enforcement linked evidence found on a rape-homicide victim to a convicted rapist’s DNA profile just eight days before he was scheduled for parole. Had he been released prior to being linked to the unsolved rape-homicide, he may very well have raped or murdered again.

By contrast, analysis and placement into CODIS of DNA profiles can dramatically enhance the chances that potential crime victims will be spared the violence of vicious, repeat offenders. The President’s initiative calls for $92.9 million to help alleviate the current backlogs of DNA samples for the most serious violent offenses – rapes, murders, and kidnappings – and for convicted offender samples needing testing. With this additional federal backlog reduction funding, the funding provided by this initiative to improve crime laboratory capacity, and continued support from the states, the current backlogs will be eliminated in five years.

Understanding the Backlog

The state and local backlog problem has two components: (1) “casework sample backlogs,” which consist of DNA samples obtained from crime scenes, victims, and suspects in criminal cases, and (2) “convicted offender backlogs,” which consist of DNA samples obtained from convicted offenders who are incarcerated or under supervision. The nature of the DNA backlog is complex and changing, and measuring the precise number of unanalyzed DNA samples is difficult.

  • Casework Sample Backlogs: In a 2001 survey of public DNA laboratories, the Bureau of Justice Statistics (BJS) found that between 1997 and 2000, DNA laboratories experienced a 73% increase in casework and a 135% increase in their casework backlogs. Many casework samples go unanalyzed for lack of a suspect to which to compare the biological evidence from the crime scene. These are often referred to as “no-suspect” cases. Based on an ongoing assessment of crime laboratories and law enforcement agencies, the National Institute of Justice (NIJ) estimates that the current backlog of rape and homicide cases is approximately 350,000. The initiative calls for $76 million in FY 2004 to help eliminate these backlogs over five years.
  • Convicted Offender Backlogs: States are increasing the number of convicted offenders required to provide DNA samples. Currently, 23 states require all convicted felons to provide DNA samples. Preliminary estimates by NIJ place the number of collected, untested convicted offender samples at between 200,000 and 300,000. NIJ also estimates that there are between 500,000 and 1,000,000 convicted offender samples that are owed, but not yet collected. The initiative calls for $15 million in FY 2004 to help eliminate convicted offender backlogs over five years.

The federal government also faces a high demand for analysis of casework and convicted offender DNA samples. The FBI has two DNA casework analysis units (see page 5). The first unit, which focuses on analyzing nuclear DNA, has a backlog of approximately 900 cases. The second unit, which focuses on analyzing mitochondrial DNA (mtDNA), has a backlog of roughly 120 cases.

The federal government also collects DNA samples from persons convicted of offenses in certain categories, including crimes of violence or terrorism. The FBI currently has a backlog of approximately 18,000 convicted offender samples. The initiative calls for $1.9 million in FY 2004 to fund the federal convicted offender program some of these funds will be devoted to eliminating the federal convicted offender backlog.

Effect of Clearing the Backlog

The results of addressing backlogs are dramatic, as the two examples below illustrate:

  • In September 1993, a married couple was attacked on a jogging trail in Dallas by a man with a gun who sexually assaulted the woman after shooting the man. No suspect was ever positively identified, although police investigated over 200 leads and 40 potential suspects. In August 2000, evidence from the case was analyzed using current DNA technology. Then, in February 2001, the DNA sample was matched to an individual who was already serving a five-year sentence for an unrelated 1997 sexual assault of a child. The man has since been convicted of capital murder and aggravated sexual assault.
  • In March 1992, an Alexandria, Virginia shop owner was stabbed more than 150 times in her home. There were no witnesses to the crime. For years, detectives had no leads, but they did have traces of someone’s blood, apparently from the fierce struggle between the victim and the killer. Meanwhile, in 1996, a man pleaded guilty to robbing a gas station, and his DNA was collected for analysis and inclusion in the Virginia DNA database. Because of the backlog, the man’s sample was not immediately analyzed. In the summer of 2000, the sample was analyzed and matched through the database to the evidence from the Alexandria woman’s murder. In April 2001, almost nine years after the commission of this brutal crime, the man was sentenced to life in prison.

Several law enforcement agencies, prosecutors’ offices, and crime labs across the country have established innovative programs to review old cases. Often called “cold case units,” these programs have enabled criminal justice officials to solve cases that have languished for years without suspects. Most frequently, DNA evidence has been the linchpin in solving these cases. For instance, this past July, a California man was found guilty of the 1974 rape-homicide of a 19 year-old pregnant woman – a case that was solved through DNA evidence nearly thirty years after the crime was committed.

Prior Federal Support of State DNA Backlog Reduction

In recent years, the federal government has strongly supported states in their efforts to eliminate backlogs of convicted offender and casework DNA samples. Since the creation in 2000 of the Department of Justice’s (DOJ’s) Convicted Offender DNA Backlog Reduction Program, more than 493,600 offender samples from 24 states have been analyzed. Since the creation in 2001 of the No Suspect Casework DNA Backlog Reduction Program, federal funds have been provided to support the analysis of approximately 24,800 cases. States have analyzed evidence in an additional 18,000 "no-suspect" cases as a result of a match requirement of Convicted Offender DNA Backlog Reduction funding.

In 2002 and 2003 combined, the President requested and Congress appropriated $70.8 million to fund these DNA backlog reduction programs. Additionally, Attorney General John Ashcroft also made available $25 million in Asset Forfeiture funds to address the backlog of convicted offender and "no suspect" casework samples. Thus, the Bush Administration already has devoted more than $95 million to reducing DNA backlogs.

At present, many of our Nation’s crime laboratories do not have the capacity necessary to analyze DNA samples in a timely fashion. Many have limited equipment resources, outdated information systems, and overwhelming case management demands. As a result, the criminal justice system as a whole is unable to reap the full benefits of DNA technology. The President’s initiative will provide federal funding to further automate and improve the infrastructure of federal, state, and local crime labs so they can process DNA samples efficiently and cost-effectively. These infrastructure improvements are critical to preventing future DNA backlogs, and to helping the criminal justice system realize the full potential of DNA technology.

Increasing the Analysis Capacity of Public Crime Labs

The President’s initiative will provide significant support to public crime labs so that these labs can update their infrastructure, automate their DNA analysis procedures, and improve their retention and storage of forensic evidence. The initiative calls for $60 million in FY 2004 funding, which will be dedicated to:

  • Providing Basic Infrastructure Support: Some public crime laboratories still need assistance to help them obtain equipment and material to conduct the basic processes of DNA analysis – extraction, quantitation, amplification and analysis – and to help them meet various accreditation requirements.
  • Building Infrastructure through Laboratory Information Management Systems: Laboratory Information Management Systems, or “LIMS,” are designed to automate evidence handling and casework management, to improve the integrity and speed of evidence handling procedures, and to ensure proper chain of custody. DOJ estimates that only 10 percent of the public DNA laboratories have LIMS systems.
  • Providing Automation Tools to Public DNA Laboratories: To streamline aspects of the DNA analysis procedure that are labor and time-intensive, crime laboratories should have automated systems, such as robotic DNA extraction units. Automated DNA analysis systems increase analyst productivity, limit human error and reduce contamination.
  • Providing Support for the Retention and Storage of Forensic Evidence: Forensic evidence must be stored in a manner that ensures its integrity and maintains its availability throughout criminal investigations and judicial proceedings. Appropriate evidence storage conditions require costly equipment such as security systems, environmental control systems, ambient temperature monitors, and de-humidifiers. The initiative will support the improvement of evidence storage capabilities.

Funding the FBI Forensic Analysis Programs

The FBI Laboratory runs several different programs for the analysis of DNA information. The Nuclear DNA Program supports federal, state, local, and international law enforcement agencies by providing advanced technical assistance within the forensic biology discipline and sub-disciplines through interrelated capabilities and expertise. The Mitochondrial DNA (mtDNA) Analysis Program is responsible for performing mtDNA analysis of forensic evidence containing small or degraded quantities of DNA on items of evidence submitted from federal, state, and local law enforcement agencies. Mitochondrial DNA is a powerful tool available for investigating cases of kidnapping, missing persons, and skeletal remains where nuclear DNA is not present. The initiative will provide funds to these two existing programs to permit them to continue their important work. In addition, the initiative will provide funds to the FBI to further expand regional mtDNA labs that will provide an alternative source for mtDNA analysis to state and local law enforcement, and allow the FBI laboratory to concentrate more of its efforts on federal cases. The initiative calls for $20.5 million in FY 2004 to fund these programs.

Funding the Combined DNA Index System

The Combined DNA Index System (CODIS), administered by the FBI, maintains DNA profiles obtained through federal, state, and local DNA sample collection programs, and makes this information available to law enforcement agencies across the country for law enforcement identification purposes. Currently, the National DNA Index System (NDIS) of CODIS contains about 1.7 million DNA profiles. The President’s initiative includes funding to complete a general redesign and upgrade of CODIS, which will increase the system's capacity to 50 million DNA profiles, reduce the search time from hours to microseconds for matching DNA profiles, and enable instant, real‑time (as opposed to weekly) searches of the database by participating forensic laboratories. The initiative calls for $9.9 million in FY 2004 to fund this program.

In order to improve the use of DNA technology to advance the cause of justice, the Attorney General will stimulate research and development of new methods of analyzing DNA samples under the President’s initiative. Also, the President has asked the Attorney General to establish demonstration projects under the initiative to further study the public safety and law enforcement benefits of fully integrating the use of DNA technology to solve crimes. Finally, the President has directed the Attorney General to create a National Forensic Science Commission to study rapidly evolving advances in all areas of the forensic sciences and to make recommendations to maximize the use of the forensic sciences in the criminal justice system. In all, the President’s initiative will devote $24.8 million in FY 2004 to fund advances in the use of DNA technology.

Improving DNA Technology

Forensic DNA analysis is rapidly evolving. Research and development of tools that will permit crime laboratories to conduct DNA analysis quickly is vital to the goal of improving the timely analysis of DNA samples. Smaller, faster, and less costly analysis tools will reduce capital investments for crime laboratories while increasing their capacity to process more cases. Over the course of the next several years, DNA research efforts will focus on the following areas:

  • The development of “DNA chip technology” that uses nanotechnology to improve both speed and resolution of DNA evidence analysis. This technology will reduce analysis time from several hours to several minutes and provide cost-effective miniaturized components.
  • The development of more robust methods to enable more crime labs to have greater success in the analysis of degraded, old, or compromised items of biological evidence.
  • Advanced applications of various DNA analysis methods, such as automated Short Tandem Repeats (STRs), Single Nucleotide Polymorphisms (SNPs), mitochondrial DNA analysis (mtDNA), and Y-chromosome DNA analysis.
  • The use of animal, plant, and microbial DNA to provide leads that may link DNA found on or near human perpetrators or victims to the actual perpetrator of the crime.
  • Technologies that will enable DNA identification of vast numbers of samples occasioned by a mass disaster or mass fatality incident.
  • Technologies that permit better separation of minute traces of male sexual assailant DNA from female victims.

The initiative devotes $10 million in FY 2004 funding to benefit the state and local criminal justice community through DNA research and development. It also requests $9.8 million in FY 2004 funding to further expand the FBI’s DNA research and development program.

Establishing DNA Demonstration Projects

To further research the impact of increased DNA evidence collection on public safety and law enforcement operations, the Attorney General will conduct rigorous scientific research through demonstration projects on the use of DNA evidence under the initiative. This research will help determine the scope of public safety benefits that result when police are trained to more effectively collect DNA evidence and prosecutors are provided with training to enhance their ability to present this evidence in court.

Several jurisdictions will be selected to incorporate core training and evidence collection requirements in their daily operations. At each site, one or more law enforcement agencies will be chosen to implement extensive training on the collection of DNA evidence and to increase the resources devoted to the investigation and prosecution of these cases. Prosecutors will also receive training on how to more effectively present DNA evidence and how forensic DNA technology may be used to solve current and “cold” cases. Jurisdictions that received increased training and resources will be compared with jurisdictions that did not receive these benefits.

The resulting comparison will measure the impact of increased DNA evidence collection on public safety and law enforcement operations. For example, projects will examine whether there are increased crime clearance rates, whether DNA aided investigations, the number of cases successfully prosecuted, the number of cases where guilty pleas were obtained due to the presence of DNA evidence, any financial savings resulting from the use of forensic evidence, and increased responsiveness to victims. The information obtained will allow state and local governments to make more informed decisions regarding investment in forensic DNA as a crime-fighting tool. The initiative calls for $4.5 million in FY 2004 to fund these projects.

Creating a National Forensic Science Commission

To facilitate the ability of policymakers to assess the needs of the forensic science community, and to stimulate public awareness of the uses of forensic technology to solve crimes, the President has directed the Attorney General to create a National Forensic Science Commission. The Commission will be charged with two primary responsibilities: (1) developing recommendations for long-term strategies to maximize the use of current forensic technologies to solve crimes and protect the public, and (2) identifying potential scientific breakthroughs that may be used to assist law enforcement.

The Attorney General will appoint Commission members from professional forensic science organizations and accreditation bodies and from the criminal justice community. These individuals will have broad knowledge and in-depth expertise in the criminal justice system and in various areas of the forensic sciences such as analytical toxicology, trace evidence, forensic biology, firearms and toolmark examinations, latent fingerprints, crime scene analysis, digital evidence, and forensic pathology, in addition to DNA. Judges, prosecutors, attorneys, victim advocates, and other members of the criminal justice system will also be represented on the Commission.

The Commission will study advances in all areas of the forensic sciences and make recommendations on how new and existing technologies can be used to improve public safety. The Commission will also serve as an ongoing forum for discussing initiatives and policy, and may issue recommendations that will assist state and local law enforcement agencies in the cost-effective use of these technologies to solve crimes. The initiative devotes $500,000 in FY 2004 to the establishment of the Commission.

In order to maximize the use of DNA technology, under the President’s initiative, the Attorney General will develop training and provide assistance regarding the collection and use of DNA evidence to the wide variety of professionals involved in the criminal justice system, including police officers, prosecutors, defense attorneys, judges, forensic scientists, medical personnel, victim service providers, corrections officers, and probation and parole officers.

Key players in the criminal justice system should receive additional training in the proper collection, preservation, and use of DNA evidence. Fundamental knowledge of the capabilities of DNA technology is essential for police officers to collect evidence properly, prosecutors and defense attorneys to introduce and use it successfully in court, and judges to rule correctly on its admissibility. Victim service providers and medical personnel likewise need to understand DNA technology in order to encourage more successful evidence collection and to be fully responsive to the needs of victims.

Law Enforcement Training

As the first responders to crime scenes, law enforcement officers should be able to identify, collect and preserve probative biological evidence for submission to crime laboratories. Improper collection can mean that valuable evidence is missed or rendered unsuitable for testing. The initiative devotes $3.5 million in FY 2004 to assist law enforcement in meeting the following training needs:

  • Basic “awareness training” on DNA evidence for patrol officers and other first-responders
  • Intensive training on identifying, collecting, and preserving potential DNA evidence for evidence technicians, investigators, and others processing crime scenes
  • Training and education for investigators and responding officers on DNA databases and their potential to provide leads in current and “cold” cases and
  • Training and information for law enforcement leadership and policymakers to facilitate more informed decisions about effective DNA evidence collection and testing.

Training Prosecutors, Defense Attorneys, and Judges

In order to achieve just results in cases involving DNA evidence, prosecutors, defense attorneys, and judges should receive proper training on the use and presentation of DNA evidence. The initiative devotes $2.5 million in FY 2004 to support:

  • Training and technical assistance for prosecutors to learn about solving “cold cases” with DNA evidence, responding to post-conviction DNA testing requests, and developing innovative legal strategies to optimize the power of forensic DNA technology. Grant funds will be available for state and local prosecutors’ organizations for the development and delivery of training materials to assist prosecutors in presenting this evidence before courts and juries, and in understanding more about the value of DNA evidence in particular cases.
  • Training for defense counsel handling cases involving biological evidence on the applications and limitations of DNA evidence. Grant funds will be made available to continuing legal education programs or bar associations to provide training and resources on forensic DNA technology.
  • Training for judges, who must be equipped with sufficient technical and scientific knowledge to make appropriate rulings in cases involving DNA evidence. Grant funds will be available to national judicial conferences and organizations.

Training For Probation and Parole Officers and Corrections Personnel

Probation and parole officers play a critical role in ensuring that offenders are complying with their statutory obligations to provide DNA samples. Corrections personnel often are responsible for obtaining DNA samples from inmates required by law to submit such samples. Through training and education programs, these professionals will be better equipped to ensure that samples are taken from all individuals who are required by law to provide them. The initiative calls for $1 million in FY 2004 to support this training.

Training for Forensic Scientists

The forensic science community has a critical need for trained forensic scientists in public crime laboratories. The initiative will assist the development of comprehensive training programs for a new generation of forensic scientists, enabling new forensic scientists to receive in-depth training to prepare them for analyzing actual casework in a crime laboratory. The initiative calls for $3 million in FY 2004 to support this training.

Training for Medical Personnel

The initiative will also provide $5 million in FY 2004 to support the development of training and educational materials for doctors and nurses involved in treating victims of sexual assault. Trained medical personnel are needed to effectively collect usable DNA evidence, while safeguarding the privacy rights and addressing the needs of rape victims requiring sexual assault exams. These programs will specifically target underserved areas of the country. Funding may also be used to support the development of SANE (Sexual Assault Nurse Examiner), SAFE (Sexual Assault Forensic Examiner), and SART (Sexual Assault Response Team) programs.

Training for Victim Service Providers

Victims and those who advocate on their behalf must have access to information about the investigative and courtroom uses of forensic DNA evidence. Victims should be properly informed about how DNA evidence may impact their cases. In situations involving post-conviction DNA testing, victim service providers must be able to assist victims through the often-painful process of newly-ordered DNA tests and re-opened court proceedings. To address the concerns of victims, the initiative would develop additional DNA education and training programs for victim advocates and victim service providers so that they may better assist victims in all cases involving DNA evidence. The initiative calls for $5 million in FY 2004 to support this training.

Hairs, Fibers, Crime, and Evidence, Part 1, by Deedrick (Forensic Science Communications, July 2000)

Hairs, which are composed primarily of the protein keratin, can be defined as slender outgrowths of the skin of mammals. Each species of animal possesses hair with characteristic length, color, shape, root appearance, and internal microscopic features that distinguish one animal from another. Considerable variability also exists in the types of hairs that are found on the body of an animal. In humans, hairs found on the head, pubic region, arms, legs, and other body areas have characteristics that can determine their origin. On animals, hair types include coarse outer hairs or guard hairs, the finer fur hairs, tactile hairs such as whiskers, and other hairs that originate from the tail and mane of an animal.

Because hairs can be transferred during physical contact, their presence can associate a suspect to a victim or a suspect/victim to a crime scene. The types of hair recovered and the condition and number of hairs found all impact on their value as evidence in a criminal investigation. Comparison of the microscopic characteristics of questioned hairs to known hair samples helps determine whether a transfer may have occurred.

Hair Microscopy

The examination of human hairs in the forensic laboratory is typically conducted through the use of light microscopy. This examination routinely involves a two-step process—the identification of questioned hairs and the comparison of questioned and known hairs. The purpose for conducting this examination is to ascertain whether two or more individuals could have come into contact or whether one or more individuals could have come into contact with an object. This associative evidence is particularly useful in crimes of violence, such as homicide, sexual assault, and aggravated assault, where physical contact may have occurred. Crimes such as burglary and armed robbery typically involve the recovery of debris and articles of clothing which may contain hairs useful for the identification of suspects.

The value of hair evidence is related to the variability of hair characteristics between individuals in the population, which can be visualized through the use of comparison microscopy. There are many factors that impact on the reliability of a hair association, including experience, training, suitability of known hair standards, and adequacy of equipment. Although hair evidence is a valuable tool in human identification, it is difficult to establish a statistical probability for a particular association due in part to the lack of reliable quantitative assessments of the microscopic characteristics present in hairs.

The comparison microscope consists of two compound light microscopes connected by an optical bridge that allows for the simultaneous viewing of questioned hairs and known hairs. Typically, a glass microscope slide containing known or reference hairs is positioned on the stage of one microscope, and a glass microscope slide containing a questioned hair or hairs is positioned on the stage of the other microscope. This enables the hair examiner to compare the microscopic characteristics of the known and questioned hairs in one field. The range of magnification used is approximately 40X to 400X.

The hair examination process involves many different steps, the first of which is to determine whether the hair in question originated from an animal or a human being. If the hair originated from an animal, it is possible to further identify it to a particular type of animal. Although certain hairs can be attributed to species, it is not possible to identify hairs to a specific animal to the exclusion of other similar animals. An example of this occurs when dog hairs can be associated to a particular breed but cannot be identified to a specific dog within that breed.

Hair Anatomy and Growth

Hair is present on many different regions of the body. Each region, such as the head, pubic area, chest, axillae, and limbs, has hairs with microscopical characteristics attributable to that region. Although it is possible to identify a hair as originating from a particular body area, the regions of the body that are primarily used in forensic comparisons are the head and pubic areas. As hairs undergo a cyclical growth (anagen) and resting phase (telogen), the visible microscopic characteristics are sufficient to determine the phase of growth of the hair.

During the anagen phase, the hair is actively growing, and materials are deposited in the hair shaft by cells found in the follicle. Metabolically active and dividing cells above and around the dermal papilla of the follicle grow upward during this phase, to form the major components of the hair—the medulla, cortex, cuticle, and accompanying root sheath. In the telogen phase, the follicle is dormant or resting. The transition period between the anagen and telogen phases is referred to as the catagen phase.

Hairs are routinely lost during the telogen phase and often become a primary source of evidentiary material. An example of this natural shedding process can be seen when one combs through the hairs on the head. It is not uncommon for hairs of this type to be transferred to another individual or to an object during physical contact. Hairs can also become dislodged from the body while they are in an actively growing state, such as by pulling or by striking with an object. The microscopical appearance of the root area will allow for the determination of the growth phase.

On a healthy head, 80 to 90 percent of the hair follicles are in the anagen phase, 2 percent are in the catagen phase, and 10 to 18 percent are in the telogen phase. Once the hair reaches the telogen phase, the follicles have achieved a mature, stable stage of quiescence. During the telogen phase, the hair is anchored in the follicle only by the root, which is club-shaped. The germ cells below the club-shaped root will give rise to the next generation of an anagen hair. The replacement of human scalp hair occurs in a scattered mosaic fashion with no apparent wave-like or seasonal pattern. The average period of growth for scalp hair is approximately 1,000 days the resting phase lasts about 100 days. Approximately 10 percent of the hairs on a human head (100/1000), therefore, are in the quiescent telogen phase, and a minimal amount of force—such as that from combing—is required to dislodge the hairs from the dormant follicle.

The basic morphology of human hairs is shared by each individual in the population, but the arrangement, distribution, and appearance of individual microscopic characteristics within different regions of hair routinely allow a skilled hair examiner to differentiate hairs between individuals. An analogy would be the ability of an individual to recognize the face of a friend or relative in a crowd even though each person in the crowd possesses ears, eyes, a nose, and a mouth.

Animal Hairs

Animal hairs discovered on items of physical evidence can link a suspect or location to a crime of violence. A victim placed in a vehicle or held at a location where animals are routinely found often results in the transfer of animal hairs to the victim’s clothing. Cat or dog hairs can be found on the adhesive portions of ransom and extortion notes prepared by pet owners. The transfer of pet hairs to the victim or crime scene may also occur when the suspect is a pet owner and has animal hairs on his or her clothing when the contact occurs. This is referred to as a secondary transfer of trace material.

When an animal hair is found, it is identified to a particular type of animal and microscopically compared with a known hair sample from either an animal hair reference collection or a specific animal. If the questioned hair exhibits the same microscopic characteristics as the known hairs, it is concluded that the hair is consistent with originating from that animal. It is noted, however, that animal hairs do not possess enough individual microscopic characteristics to be associated with a particular animal to the exclusion of other similar animals.

Animal hairs found at crime scenes or on the clothing of suspects and victims may also have originated from a fur coat or pelt. These hairs may have been artificially colored or trimmed and often do not have a root. It is preferred that the entire fur garment be obtained so that suitable known samples can be submitted for comparison.

Human Hairs

As stated previously, physical contact may result in the transfer of hairs. These can transfer directly from the region of the body where they are growing—a primary transfer—or they can transfer from the clothing of individuals—a secondary transfer. It has been reported that approximately 100 head hairs are shed by an individual each day. These hairs are shed on clothing and on items in the environment. Contact between a victim and a suspect’s environment can easily cause a secondary transfer of hair. Hairs that are found on the clothing of suspects or victims and appear to have fallen out naturally may be the result of primary or secondary transfer. Hairs that have been forcibly removed may suggest a violent confrontation.

Body Area Determination

The body area from which a hair originated can be determined by general morphology. Length, shape, size, color, stiffness, curliness, and microscopic appearance all contribute to the determination of body area. Pigmentation and medullar appearance also influence body area identification. Hairs that exhibit microscopic characteristics shared by different anatomical areas are often referred to as body hairs. These include hairs found on the upper legs, lower abdomen, and back. Because there is a wide range of interpersonal variation in head and pubic hairs, the majority of work in forensics has been in comparing and differentiating hairs from the head and pubic regions.

Head Hairs
Head hairs are usually the longest hairs on the human body. They are characterized as having a uniform diameter and, often, a cut tip. Head hairs can appear uncut, with tapered tips but are more often cut with scissors, razors, or clippers. In general these hairs are subject to more alteration than hairs from other body areas. Alterations to the natural appearance of hair include use of hair dyes, rinses, permanents, frosts, and other chemical applications. Environmental alterations can result from exposure to excessive sunlight, wind, dryness, and other conditions. Because these hairs can be affected by a number of environmental and chemical conditions, it is recommended that head hair samples be obtained as soon as possible from suspects and victims of crime. Head hair samples obtained years after a crime are generally not suitable for meaningful comparison purposes.

As head hairs are routinely compared in a forensic laboratory, it is important to obtain suitable known samples from suspects and victims and possibly from other individuals (elimination samples). The known sample should contain a random sampling of hair from different areas of the scalp. The number of hairs required for a meaningful comparison may vary depending on the uniformity of characteristics present in the hairs from an individual. Because this is not known when the hair sample is taken, obtain at least 25 full-length hairs. This hair sample should include both plucked and combed hairs, packaged separately.

Pubic hairs are generally coarse and wiry in appearance. They exhibit considerable diameter variation or buckling and often have a continuous to discontinuous medulla. While tapered tips are common, these hairs may also be abraded or cut.

Facial Hairs
Facial hairs are more commonly called beard hairs or mustache hairs. These hairs are coarse in appearance and can have a triangular cross section. Heavy shouldering or troughs in the hair are observed under magnification. Other characteristics include a wide medulla and a razor-cut tip.

The presence of facial hairs on the clothing of a suspect or victim may help establish contact between these individuals. While these hairs may be compared microscopically, the significance of the association may not be as great as head hair and pubic hair associations.

Limb Hairs
Hairs from the legs and arms constitute limb hairs. These hairs are shorter in length, arc-like in shape, and often abraded or tapered at the tips. The pigment in limb hair is generally granular in appearance, and the medulla is trace to discontinuous.

While limb hairs are not routinely compared in a forensic laboratory, they can differ in appearance between individuals. These differences, however, are not considered sufficient to allow limb hairs to be of value for meaningful comparison purposes. The presence of leg or arm hairs on certain items of evidence may help to corroborate other investigative information.

Fringe Hairs
Hairs originating from areas of the body outside those specifically designated as head or pubic are generally not suitable for significant comparison purposes. These hairs might originate from the neck, sideburns, abdomen, upper leg, and back.

Other Body Area Hairs
Axillary (underarm) hairs, chest hairs, eye hairs, and nose hairs are not routinely compared. As with limb hairs and fringe hairs, their presence may help to corroborate information obtained during an investigation.

A human hair can be associated with a particular racial group based on established models for each group. Forensic examiners differentiate between hairs of Caucasoid (European ancestry), Mongoloid (Asian ancestry), and Negroid (African ancestry) origin, all of which exhibit microscopic characteristics that distinguish one racial group from another. Head hairs are generally considered best for determining race, although hairs from other body areas can be useful. Racial determination from the microscopic examination of head hairs from infants, however, can be difficult, and hairs from individuals of mixed racial ancestry may possess microscopic characteristics attributed to more than one racial group.

The identification of race is most useful as an investigative tool, but it can also be an associative tool when an individual’s hairs exhibit unusual racial characteristics.

Caucasoid (European)
Hairs of Caucasoid or Caucasian origin can be of fine to medium coarseness, are generally straight or wavy in appearance, and exhibit colors ranging from blonde to brown to black. The hair shafts of Caucasian hairs vary from round to oval in cross section and have fine to medium-sized, evenly distributed pigment granules.

Mongoloid (Asian)
Hairs of Mongoloid or Asian origin are regularly coarse, straight, and circular in cross section, with a wider diameter than the hairs of the other racial groups. The outer layer of the hair, the cuticle, is usually significantly thicker than the cuticle of Negroid and Caucasian hairs, and the medulla, or central canal, is continuous and wide. The hair shaft, or cortex, of Mongoloid hair contains pigment granules that are generally larger in size than the pigment granules of Caucasian hairs and which often appear to be grouped in patchy areas within the shaft. Mongoloid hair can have a characteristic reddish appearance as a product of its pigment.

Negroid (African)
Hairs of Negroid or African origin are regularly curly or kinky, have a flattened cross section, and can appear curly, wavy, or coiled. Negroid pigment granules are larger than those found in Mongoloid and Caucasian hair and are grouped in clumps of different sizes and shapes. The density of the pigment in the hair shaft may be so great as to make the hair opaque. A Negroid hair shaft exhibits variation or apparent variation in diameter because of its flattened nature and the manner in which it lies on the microscope slide. Twisting of the hair shaft, known as buckling, can be present, and the hair shaft frequently splits along the length.

The age of an individual cannot be determined definitively by a microscopic examination however, the microscopic appearance of certain human hairs, such as those of infants and elderly individuals, may provide a general indication of age. The hairs of infants, for example, are generally finer and less distinctive in microscopic appearance. As individuals age, hair can undergo pigment loss and changes in the configuration of the hair shaft to become much finer and more variable in diameter.

Although the sex of an individual is difficult to determine from microscopic examination, longer, treated hairs are more frequently encountered in female individuals. Sex can be determined from a forcibly removed hair (with tissue), but this is not routinely done. Definitive determination of sex can be accomplished through the staining of sex chromatin in the cells found in the follicular tissue, but nuclear DNA and mitochondrial DNA (mtDNA) tests will provide more specific information regarding the possible origin of the hair.

Treatment and Removal

The presence of artificial treatment such as dyes or rinses can be identified through microscopical examination. Inasmuch as head hairs grow at the rate of one centimeter per month, the approximate time of this treatment can be determined by measuring the length of untreated area of the hair. A direct, side-by-side comparison of the color of the questioned and known artificially treated hairs is typically conducted by a hair examiner.

As stated previously, the condition of the root area of a hair allows the hair examiner to microscopically determine whether the hair was forcibly removed from the body or shed naturally. Hairs that fall out naturally have a club-shaped root, whereas a forcibly removed hair will be stretched and may have tissue attached to it. The manner in which a hair was removed can have considerable value, especially when there is a possibility of violent contact between a suspect and a victim. The identification of burned, cut, or crushed hairs can also be established through microscopic examination.

Biological or Environmental Alteration

The microscopic appearance of hairs is affected by natural biological fluctuations and environmental influences. For this reason, it is important that known hair standards are collected contemporaneously to the deposition of questioned hairs. Head hairs are most affected by these factors, whereas pubic hairs are less influenced. A time period of several months to years can detract from a meaningful head hair comparison, whereas several years may not severely impact on meaningful pubic hair comparisons.

When hairs originate from a body in a state of decomposition, a dark band may appear near the root of the hair. This characteristic has been labeled a postmortem root band.


There are several possible conclusions that can be reached from the microscopic examination and comparison of human hairs. When the questioned hair(s) is compared to the known hairs using a comparison microscope, the full length of the hair(s) as well as the full range of microscopic characteristics must be considered. Following their analyses, hair examiners may conclude the following:

  • The questioned hair exhibits the same microscopic characteristics as the hairs in the known hair sample and, accordingly, is consistent with originating from the source of the known hairs.
  • The questioned hair is microscopically dissimilar to the hairs found in the known hair sample and, accordingly, cannot be associated to the source of the known hairs.
  • Similarities and slight differences were observed between the questioned hair and hairs in the known hair sample. Accordingly, no conclusion could be reached as to whether the questioned hair originated from the same source as the known hairs.

When a hair exhibits the same microscopic characteristics as hairs in the known hair sample, a qualifying statement may be added to the report. This statement may read as follows:

Hair comparisons are not a basis for absolute personal identification. It should be noted, however, that because it is unusual to find hairs from two different individuals that exhibit the same microscopic characteristics, a microscopic association or match is the basis for a strong association.

Significance of Hair Evidence

The significance of hair examination results is dependent on the method of evidence collection used at the crime scene, the evidence processing techniques employed, the methodology of the hair examination process, and the experience of the hair examiner. Head hairs and pubic hairs are routinely held as more significant than hairs from other body areas.

Questions concerning hair examinations and their significance include:

  • Is the significance of a hair association dependent on a set number of compared characteristics?
  • Does the length of the compared hairs affect the significance of an association?
  • Does treatment influence the significance?
  • Are hairs of specific racial groups more significant than others?
  • Do hair sprays, gels, or other hair applications influence the significance of a hair match?
  • Is a hair match significant when the comparison was made with a limited number of known hairs? 

The hair identification process involves the examination and comparison of hair characteristics along the entire length of the hair(s). Longer hairs have more characteristics to compare, and the greater the variation along the length, the greater the degree of significance.

The value of the evidence in establishing a particular association can be influenced by

  • the probability that the association (or elimination)
    was due to coincidence,
  • the probability that the association (or elimination)
    was due to examiner error, and
  • the probability that there is an alternative
    explanation for the evidence, such as secondary transfer,
    contamination, or deliberate planting.

The significance of a hair match is influenced by how often the examiner has seen certain characteristics as well as by how often the examiner has seen hairs of a particular race or body area.

The range of opinions concerning hair examinations includes:

  • Nothing about hair is comparable to the specificity of fingerprints, and at best, the probability of establishing identification from hair is no greater than the probability of determining identification using the ABO blood group system
  • Research studies have shown that hairs from two individuals are distinguishable that no accidental or coincidental matches occurred and that such accidental or coincidental matches would, in actual casework, be a relatively rare event and
  • The significance of a hair match is a median point between the above statements.

It has also been stated that hair evidence is only of value when used in conjunction with other evidence.

Positive hair comparison conclusions may be weakened by the presence of incomplete hairs by common, featureless hairs and by known samples with large intrasample variation. Conversely, positive hair comparison conclusions are strengthened by the presence of two or more mutually dissimilar hairs that are similar to a known sample by hairs with unusual characteristics by two-way transfers and by additional examinations of confirmation, such as DNA and sex-typing.

Normal negative hair comparison conclusions are weakened by deficiencies in the known hair sample, including too few hairs, unrepresentative hairs, incomplete hairs, and a significant temporal difference between the offense and the collection of the known sample. Negative hair comparison conclusions are also weakened by the presence of incomplete questioned hairs and by similarities and differences within the hair sample.

Factors which strengthen normal negative hair comparison conclusions include a large quantity of known sample hairs little intrasample variation within the known sample and hairs that are very dissimilar, such as those exhibiting distinct racial and/or microscopic characteristics. Two or more questioned hairs that are found together in a clump and are dissimilar to the known sample will also support a negative hair comparison conclusion.

What does it mean to be genetically Jewish?

W hen my parents sent their saliva away to a genetic testing company late last year and were informed via email a few weeks later that they are both “100% Ashkenazi Jewish”, it struck me as slightly odd. Most people I know who have done DNA tests received ancestry results that correspond to geographical areas – Chinese, British, West African. Jewish, by comparison, is typically parsed as a religious or cultural identity. I wondered how this was traceable in my parents’ DNA.

After arriving in eastern Europe around a millennium ago, the company’s website explained, Jewish communities remained segregated, by force and by custom, mixing only occasionally with local populations. Isolation slowly narrowed the gene pool, which now gives modern Jews of European descent, like my family, a set of identifiable genetic variations that set them apart from other European populations at a microscopic level.

This genetic explanation of my Ashkenazi Jewish ancestry came as no surprise. According to family lore, my forebears lived in small towns and villages in eastern Europe for at least a few hundred years, where they kept their traditions and married within the community, up until the Holocaust, when they were either murdered or dispersed.

But still, there was something disconcerting about our Jewishness being “confirmed” by a biological test. After all, the reason my grandparents had to leave the towns and villages of their ancestors was because of ethno-nationalism emboldened by a racialized conception of Jewishness as something that exists “in the blood”.

The raw memory of this racism made any suggestion of Jewish ethnicity slightly taboo in my family. If I ever mentioned that someone “looked Jewish” my grandmother would respond, “Oh really? And what exactly does a Jew look like?” Yet evidently, this wariness of ethnic categorization didn’t stop my parents from sending swab samples from the inside of their cheeks off to a direct-to-consumer genetic testing company. The idea of having an ancient identity “confirmed” by modern science was too alluring.

Not that they’re alone. As of the beginning of this year, more than 26 million people have taken at-home DNA tests. For most, like my parents, genetic identity is assimilated into an existing life story with relative ease, while for others, the test can unearth family secrets or capsize personal narratives around ethnic heritage.

But as these genetic databases grow, genetic identity is reshaping not only how we understand ourselves, but how we can be identified by others. In the past year, law enforcement has become increasingly adept at using genetic data to solve cold cases a recent study shows that even if you haven’t taken a test, chances are you can be identified by authorities via genealogical sleuthing.

What is perhaps more concerning, though, is how authorities around the world are also beginning to use DNA to not only identify individuals, but to categorize and discriminate against entire groups of people.

In February of this year, the Israeli newspaper Haaretz, reported that the Chief Rabbinate of Israel, the peak religious authority in the country, had been requesting DNA tests to confirm Jewishness before issuing some marriage licenses.

In Israel, matrimonial law is religious, not civil. Jews can marry Jews, but intermarriage with Muslims or Christians is legally unacknowledged. This means that when a Jewish couple want to tie the knot, they are required by law to prove their Jewishness to the Rabbinate according to Orthodox tradition, which defines Jewish ancestry as being passed down through the mother.

While for most Israeli Jews this simply involves handing over their mother’s birth or marriage certificate, for many recent immigrants to Israel, who often come from communities where being Jewish is defined differently or documentation is scarce, producing evidence that satisfies the Rabbinate’s standard of proof can be impossible.

In the past, confirming Jewishness in the absence of documentation has involved contacting rabbis from the countries where people originate or tracking genealogical records back to prove religious continuity along the matrilineal line. But as was reported in Haaretz, and later confirmed by David Lau, the Ashkenazi chief rabbi of Israel, in the past year, the rabbis have been requesting that some people undergo a DNA test to verify their claim before being allowed to marry.

For many Israelis, news that the rabbinical judges were turning to DNA testing was shocking, but for Seth Farber, an American-born Orthodox rabbi, it came as no surprise. Farber, who has been living in Israel since the 1990s, is the director of Itim, the Jewish Life Information Center, an organization that helps Israeli Jews navigate state-administered matters of Jewish life, like marriage and conversion. In the past year, the organization has seen up to 50 cases where families have been asked to undergo DNA tests to certify their Jewishness.

Those being asked to take these tests, Farber told me, are mostly Russian-speaking Israelis, members of an almost 1 million-strong immigrant community who began moving to Israel from countries of the former Soviet Union in the 1990s. Due to the fact that Jewish life was forcefully suppressed during the Soviet era, many members of this community lack the necessary documentation to prove Jewishness through matrilineal descent. This means that although most self-identify as Jewish, hundreds of thousands are not considered so by the Rabbinate, and routinely have their Jewish status challenged when seeking religious services, including marriage.

For almost two decades, Farber and his colleagues have advocated for this immigrant community in the face of what they see as targeted discrimination. In cases of marriage, Farber acts as a type of rabbinical lawyer, pulling together documentation and making a case for his clients in front of a board of rabbinical judges. He fears that DNA testing will place even more power in the hands of the Rabbinate and further marginalize the Russian-speaking community. “It’s as if the rabbis have become technocrats,” he told me. “They are using genetics to give validity to their discriminatory practices.”

Despite public outrage and protests in central Tel Aviv, the Rabbinate have not indicated any intention of ending DNA testing, and reports continue to circulate in the Israeli media of how the test is being used. One woman allegedly had to ask her mother and aunt for genetic material to prove that she was not adopted. Another man was asked to have his grandmother, sick with dementia, take a test.

A protest against DNA testing in Tel Aviv. Photograph: Boris Shindler

Boris Shindler, a political activist and active member of the Russian-speaking community, told me that he believes that the full extent of the practice remains unknown, because many of those who have been tested are unwilling to share their stories publicly out of a sense of shame. “I was approached by someone who was married in a Jewish ceremony maybe 15, 20 years ago, who recently received an official demand saying if you want to continue to be Jewish, we’d like you to do a DNA test,” Shindler said. “They said if she doesn’t do it then she has to sign papers saying she is not Jewish. But she is too humiliated to go to the press with this.”

What offends Shindler most is that the technique is being used to single out his community, which he sees as part of a broader stigmatization of Russian-speaking immigrants in Israeli society as unassimilated outsiders and second-class citizens. “It is sad because in the Soviet Union we were persecuted for being Jewish and now in Israel we’re being discriminated against for not being Jewish enough,” he said.

As well as being deeply humiliating, Shindler told me that there is confusion around what being genetically Jewish means. “How do they decide when someone becomes Jewish,” he asked. “If I have 51% Jewish DNA does that mean I’m Jewish, but if I’m 49% I’m not?”

But according to Yosef Carmel, an Orthodox rabbi and co-head of Eretz Hemdah, a Jerusalem-based institute that trains rabbinical judges for the Rabbinate, this is a misunderstanding of how the DNA testing is being used. He explained that the Rabbinate are not using a generalized Jewish ancestry test, but one that screens for a specific variant on the mitochondrial DNA – DNA that is passed down through the mother – that can be found almost exclusively in Ashkenazi Jews.

A number of years ago Carmel consulted genetic experts who informed him that if someone bears this specific mitochondrial DNA marker, there is a 90 to 99% chance that this person is of Ashkenazi ancestry. This was enough to convince him to pass a religious ruling in 2017 that states that this specific DNA test can be used to confirm Jewishness if all other avenues have been exhausted, which now constitutes the theological justification for the genetic testing.

For David Goldstein, professor of medical research in genetics at Columbia University whose 2008 book, Jacob’s Legacy: A Genetic View of Jewish History, outlines a decade’s worth of research into Jewish population genetics, translating scientific insights about small genetic variants in the DNA to normative judgments about religious or ethnic identity is not only problematic, but misunderstands what the science actually signals.

“When we say that there is a signal of Jewish ancestry, it’s a highly specific statistical analysis done over a population,” he said. “To think that you can use these type of analyses to make any substantive claims about politics or religion or questions of identity, I think that it’s frankly ridiculous.”

But others would disagree. As DNA sequencing becomes more sophisticated, the ability to identify genetic differences between human populations has improved. Geneticists can now locate variations in the DNA so acutely as to differentiate populations living on opposite sides of a mountain range.

In recent years, a number of high-profile commentators have appropriated these scientific insights to push the idea that genetics can determine who we are socially, none more controversially than the former New York Times science writer Nicholas Wade. In his 2014 book, A Troublesome Inheritance: Genes, Race and Human History, Wade argues that genetic differences in human populations manifest in predictable social differences between those groups.

His book was strongly denounced by almost all prominent researchers in the field as a shoddy incarnation of race science, but the idea that our DNA can determine who we are in some social sense has also crept into more mainstream perspectives.

In an op-ed published in the New York Times last year, the Harvard geneticist David Reich argued that although genetics does not substantiate any racist stereotypes, differences in genetic ancestry do correlate to many of today’s racial constructs. “I have deep sympathy for the concern that genetic discoveries could be misused to justify racism,” he wrote. “But as a geneticist I also know that it is simply no longer possible to ignore average genetic differences among ‘races’.”

Reich’s op-ed was shared widely and drew condemnation from other geneticists and social science researchers.

In an open letter to Buzzfeed, a group of 67 experts also criticized Reich’s careless communication of his ideas. The signatories worried that imprecise language within such a fraught field of research would make the insights of population genetics more susceptible to being “misunderstood and misinterpreted”, lending scientific validity to racist ideology and ethno-nationalist politics.

And indeed, this already appears to be happening. In the United States, white nationalists have channeled the ideals of racial purity into an obsession with the reliability of direct-to-consumer DNA testing. In Greece, the neo-fascist Golden Dawn party regularly draw on studies on the origins of Greek DNA to “prove” 4,000 years of racial continuity and ethnic supremacy.

Most concerning is how the conflation of genetics and racial identity is being mobilized politically. In Australia, the far-right One Nation party recently suggested that First Nations people be given DNA tests to “prove” how Indigenous they are before receiving government benefits. In February, the New York Times reported that authorities in China are using DNA testing to determine whether someone is of Uighur ancestry, as part of a broader campaign of surveillance and oppression against the Muslim minority.

While DNA testing in Israel is still limited to proving Jewishness in relation to religious life, it comes at a time when the intersections of ethnic, political and religious identity are becoming increasingly blurry. Just last year, Benjamin Netanyahu’s government passed the Nation State law, which codified that the right to national self-determination in the country is “unique to the Jewish people”.

Shlomo Sand, an Israeli historian who has written extensively on the politics of Jewish population genetics, worries that if DNA testing is normalized by the Rabbinate, it could be used to confirm citizenship in the future. “Israeli society is becoming more of a closed, ethno-centric society,” he said. “I am worried that people will start to use this genetic testing to build this political national identity.”

For Sand, there is a particularly dark irony that this type of genetic discrimination is being weaponized by Jews against other Jews. “I am the descendant of Holocaust survivors, people who suffered because of biological and essentialist attitudes to human groups,” he told me. “When I hear stories of people using DNA to prove that you are a Jew, or French, or Greek, or Finnish, I feel like the Nazis lost the war, but they won the victory of an ideology of essentialist identity through the blood.”

But for Seth Farber, the problem with a DNA test for Jewishness runs deeper than politics it contravenes what he believes to be the essence of Jewish identity. There is a specific principle in Jewish law, he told me, that instructs rabbis not to undermine someone’s self-declared religious identity if that person has been accepted by a Jewish community. The central principle is that when it comes to Jewish identity, the most important determinants are social – trust, kinship, commitment – not biological. “Our tradition has always been that if someone lives among us and partakes in communal and religious life, then they are one of us,” Farber said. “Just because we have 23andMe doesn’t mean that we should abandon this. That would be an unwarranted and radical reinterpretation of Jewish law.”

As I was reporting this story, it often struck me as oxymoronic that an institution like the Rabbinate would embrace new technology to uphold an ancient identity. It seemed to contradict the very premise of Orthodoxy, which, by definition, is supposed to rigidly maintain tradition in the face of all that is new and unknown.

But Jessica Mozersky, assistant professor of medicine at Washington University in St Louis, explained that part of the reason why the Rabbinate might be comfortable with using DNA to confirm Jewishness is because of an existing familiarity with genetic testing in the community to screen for rare genetic conditions. “Because Ashkenazi communities have a history of marrying in, they have this high risk for certain heritable diseases and have established genetic screening programs,” she explained. “So this has made it less fraught and problematic to talk about Jewish genetics in Ashkenazi communities.”

In fact, the Orthodox Jewish community is so comfortable with the idea of genetic identity that they have even put together their own international genetic database called Dor Yeshorim, which acts as both a dating service and public health initiative. When two members of the community are being set up for marriage, Mozersky explained, the matchmaker will check whether or not they are genetically compatible on the DNA database. “This means that the notion of genetics as a part of identity is deeply interwoven in many ways with communal life,” she said.

This is something I could identify with. When I was 16 and attending a Jewish day-school in Melbourne, Australia, we had what was called “mouth-swab day”. Everyone in my grade gathered on the basketball courts to provide spit samples that were sent off and screened for Tay-Sachs disease, a rare inherited disorder significantly more common among Ashkenazi Jews that eats away at the nerve cells in the brain and spinal cord. As we waited in line, we joked that this was our punishment for our ancestors marrying their cousins.

A few weeks later, after we got the results, I told my grandmother about “mouth-swab day”. I was interested in her thoughts on my newly discovered genetic identity, which seemed to connect me biologically to the world she grew up in, a world of insularity, religiosity, tradition, and trauma.

“It’s like I’ve always said,” she declared, after I told her that I wasn’t a carrier of this rare genetic mutation. “It’s important to mix the blood.”

1. Get a sample of DNA

DNA is found in most cells of the body, including white blood cells, semen, hair roots and body tissue. Traces of DNA can also be detected in body fluids, such as saliva and perspiration because they also contain epithelial cells. Forensic scientists and Police officers collect samples of DNA from crime scenes. DNA can also be collected directly from a person using a mouth swab (which collects inner cheek cells). Find out more in the article Crime scene evidence.

2. Extract the DNA

DNA is contained within the nucleus of cells. Chemicals are added to break open the cells, extract the DNA and isolate it from other cell components.

3. Copy the DNA

Often only small amounts of DNA are available for forensic analysis so the STRs at each genetic locus are copied many times using the polymerase chain reaction (PCR) to get enough DNA to make a profile. Find out more in the article What is PCR?

Specific primers are used during PCR that attach a fluorescent tag to the copied STRs.

4. Determine the size of the STRs

The size of the STRs at each genetic locus is determined using a genetic analyser. The genetic analyser separates the copied DNA by gel electrophoresis and can detect the fluorescent dye on each STR. This is the same piece of equipment used in the lab for DNA sequencing.

5. Is there a match?

The number of times a nucleotide sequence is repeated in each STR can be calculated from the size of the STRs. A forensic scientist can use this information to determine if a body fluid sample comes from a particular person.

If two DNA profiles from different samples are the same, the chance that the samples came from different people is low. This provides strong evidence that the samples have a common source.

Mixed connective tissue disease

People with mixed connective tissue disease (MCTD) have symptoms that overlap with several connective tissue disorders, including systemic lupus erythematosus, polymyositis, scleroderma, and rheumatoid arthritis. [3]

A condition called Raynaud's phenomenon sometimes occurs months or years before other symptoms of MCTD develop. Most people with MCTD have pain in multiple joints, and/or inflammation of joints ( arthritis ). Muscle weakness, fevers, and fatigue are also common. [3]

  • Accumulation of fluid in the tissue of the hands that causes puffiness and swelling (edema)
  • Skin findings including lupus-like rashes (including reddish brown patches), reddish patches over the knuckles, violet coloring of the eyelids, loss of hair (alopecia), and dilation of small blood vessels around the fingernails (periungual telangiectasia)
  • Dysfunction of the esophagus (hypomotility)
  • Abnormalities in lung function which may lead to breathing difficulties, and/or pulmonary hypertension
  • Heart involvement (less common in MCTD than lung problems) including pericarditis, myocarditis, and aortic insufficiency
  • Kidney disease
  • Neurologic abnormalities (in about 10 percent of people with MCTD) such as blood vessel narrowing causing "vascular" headaches a mild form of meningitis seizures blockage of a cerebral vessel (cerebral thrombosis) or bleeding and/or various sensory disturbances in multiple areas of the body (multiple peripheral neuropathies )
  • Anemia and leukopenia (in 30 to 40 percent of cases) , enlargement of the spleen (splenomegaly), enlargement of the liver (hepatomegaly), and/or intestinal involvement in some cases

This table lists symptoms that people with this disease may have. For most diseases, symptoms will vary from person to person. People with the same disease may not have all the symptoms listed. This information comes from a database called the Human Phenotype Ontology (HPO) . The HPO collects information on symptoms that have been described in medical resources. The HPO is updated regularly. Use the HPO ID to access more in-depth information about a symptom.

Herbal Supplements Are Often Not What They Seem

Americans spend an estimated $5 billion a year on unproven herbal supplements that promise everything from fighting off colds to curbing hot flashes and boosting memory. But now there is a new reason for supplement buyers to beware: DNA tests show that many pills labeled as healing herbs are little more than powdered rice and weeds.

Using a test called DNA barcoding, a kind of genetic fingerprinting that has also been used to help uncover labeling fraud in the commercial seafood industry, Canadian researchers tested 44 bottles of popular supplements sold by 12 companies. They found that many were not what they claimed to be, and that pills labeled as popular herbs were often diluted — or replaced entirely — by cheap fillers like soybean, wheat and rice.

Consumer advocates and scientists say the research provides more evidence that the herbal supplement industry is riddled with questionable practices. Industry representatives argue that any problems are not widespread.

For the study, the researchers selected popular medicinal herbs, and then randomly bought different brands of those products from stores and outlets in Canada and the United States. To avoid singling out any company, they did not disclose any product names.

Among their findings were bottles of echinacea supplements, used by millions of Americans to prevent and treat colds, that contained ground up bitter weed, Parthenium hysterophorus, an invasive plant found in India and Australia that has been linked to rashes, nausea and flatulence.

Two bottles labeled as St. John’s wort, which studies have shown may treat mild depression, contained none of the medicinal herb. Instead, the pills in one bottle were made of nothing but rice, and another bottle contained only Alexandrian senna, an Egyptian yellow shrub that is a powerful laxative. Gingko biloba supplements, promoted as memory enhancers, were mixed with fillers and black walnut, a potentially deadly hazard for people with nut allergies.

Of 44 herbal supplements tested, one-third showed outright substitution, meaning there was no trace of the plant advertised on the bottle — only another plant in its place.

Many were adulterated with ingredients not listed on the label, like rice, soybean and wheat, which are used as fillers.

In some cases, these fillers were the only plant detected in the bottle — a health concern for people with allergies or those seeking gluten-free products, said the study’s lead author, Steven G. Newmaster, a biology professor and botanical director of the Biodiversity Institute of Ontario at the University of Guelph.

The findings, published in the journal BMC Medicine, follow a number of smaller studies conducted in recent years that have suggested a sizable percentage of herbal products are not what they purport to be. But because the latest findings are backed by DNA testing, they offer perhaps the most credible evidence to date of adulteration, contamination and mislabeling in the medicinal supplement industry, a rapidly growing area of alternative medicine that includes an estimated 29,000 herbal products and substances sold throughout North America.

“This suggests that the problems are widespread and that quality control for many companies, whether through ignorance, incompetence or dishonesty, is unacceptable,” said David Schardt, a senior nutritionist at the Center for Science in the Public Interest, an advocacy group. “Given these results, it’s hard to recommend any herbal supplements to consumers.”

Representatives of the supplement industry said that while mislabeling of supplements was a legitimate concern, they did not believe it reached the extent suggested by the new research.

Stefan Gafner, the chief science officer at the American Botanical Council, a nonprofit group that promotes the use of herbal supplements, said the study was flawed, in part because the bar-coding technology it used could not always identify herbs that have been purified and highly processed.

“Over all, I would agree that quality control is an issue in the herbal industry,” Dr. Gafner said. “But I think that what’s represented here is overblown. I don’t think it’s as bad as it looks according to this study.”

The Food and Drug Administration has used bar-coding technology to warn and in some cases prosecute sellers of seafood found to be “misbranded.” The DNA technique has also been used in studies of herbal teas, which showed that a significant percentage contain herbs and ingredients that are not listed on their labels.

But policing the supplement industry is a special challenge. The F.D.A. requires that companies test the products they sell to make sure that they are safe. But the system essentially operates on the honor code. Unlike prescription drugs, supplements are generally considered safe until proved otherwise.

Under a 1994 law, they can be sold and marketed with little regulatory oversight, and they are pulled from shelves generally only after complaints of serious injury. The F.D.A. audits a small number of companies, but even industry representatives say more oversight is needed.

“The regulations are very appropriate and rigorous,” said Duffy MacKay of the Council for Responsible Nutrition, a supplement industry trade group. “But we need a strong regulator enforcing the full force of the law. F.D.A. resources are limited, and therefore enforcement has not historically been as rigorous as it could be.”

Shelly Burgess, a spokeswoman for the F.D.A., said that companies were required to adhere to a set of good manufacturing practices designed to prevent adulteration, but that many were ignoring the rules.

“Unfortunately, we are seeing a very high percentage — approximately 70 percent — of firms’ noncompliance,” she said, “and we are very active in taking enforcement actions against such violations.”

DNA bar coding was developed about a decade ago at the University of Guelph. Instead of sequencing entire genomes, scientists realized that they could examine genes from a standardized region of every genome to identify species of plants and animals. These short sequences can be quickly analyzed — much like the bar codes on the items at a supermarket — and compared with others in an electronic database. An electronic reference library at Guelph, called the International Barcode of Life Project, contains over 2.6 million bar code records for almost 200,000 species of plants and animals.

The testing technique is not foolproof. It can identify the substances in a supplement, but it cannot determine their potency. And because the technology relies on the detection of DNA, it may not be able to identify concentrated chemical extracts that do not contain genetic material, or products in which the material has been destroyed by heat and processing.

But Dr. Newmaster emphasized that only powders and pills were used in the new research, not extracts. In addition, the DNA testing nearly always detected some plant material in the samples — just not always the plant or herb named on the label.

Some of the adulteration problems may be inadvertent. Cross-contamination can occur in fields where different plants are grown side by side and picked at the same time, or in factories where the herbs are packaged. Dr. Gafner of the American Botanical Council said that rice, starch and other compounds were sometimes added during processing to keep powdered herbs from clumping, just as kernels of rice are added to salt shakers.

But that does not explain many of the DNA results. For instance, the study found that one product advertised as black cohosh — a North American plant and popular remedy for hot flashes and other menopause symptoms — actually contained a related Asian plant, Actaea asiatica, that can be toxic to humans.

Those findings mirror a similar study of black cohosh supplements conducted at Stony Brook University medical center last year. Dr. David A. Baker, a professor of obstetrics, gynecology and reproductive medicine, bought 36 black cohosh supplements from online and chain stores. Bar coding tests showed that a quarter of them were not black cohosh, but instead contained an ornamental plant from China.