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Indirect DNA Transfer Can Result in Miscarriages of Justice

DNA Evidence Is Not as Infallible in Identifying Perpetrator as Most Believe

by David M. Reutter

Deoxyribonucleic acid (“DNA”) is regarded as the “gold standard” of forensic evidence. It is considered to be virtually indisputable evidence by juries and even judges when presented to identify an individual as having contact with a piece of evidence. A 2005 Gallup poll found 85% of Americans considered DNA to be very or completely reliable. One study found that jurors rated DNA evidence 95% accurate and between 90% and 94% persuasive, depending on where the DNA was found. The public’s faith in DNA evidence can be shaken but only when shown the lab performing the DNA testing has a history of errors.

While DNA is arguably incontrovertible evidence of identity, advances in DNA technology have raised crucial questions that go beyond simply linking a specific person to a DNA sample, which include how and when did the DNA arrive at the location it was found? Studies have proven that DNA can be found in a location or on an object that was never touched by the person who the DNA identified. That startling fact has forced the medicolegal system to consider whether the DNA evidence in question was transferred via primary, secondary, or tertiary means.

Primary DNA transfer is defined as the direct passage of DNA to objects and people. Secondary transfer is an extension of this process, where DNA is transferred to an object or person through an intermediary. Tertiary transfer occurs when there is indirect transfer through two intermediaries. “For example, one person touches a doorknob, and then a second person touches the doorknob. The second person then handles a knife. DNA could then be transferred from the first person to the doorknob, to the second person who deposits the first person’s DNA on the knife,” explains The latter two types of transfers can result in innocent people being falsely linked to a crime scene and result in the perpetrator not being convicted due to foreign DNA contaminating the forensic sample.

“It’s scary,” said Cynthia Cale, the lead forensic DNA analysis at Strand Diagnostics. “Analysts need to be aware this can happen, and they need to be able to go into court and effectively present this evidence. They need to school the jury and judge that there are other explanations for this DNA to be there.”

Expert evidence related to the question of identity DNA falls squarely within the ambit of standard forensic DNA analysis. The issue of how it got there and when, however, is different because it has been left to judges and juries to determine. When a case is based on circumstantial evidence, it is often the ultimate issue.

As early as the 1920s, it was suggested that individuals could deposit and take trace evidence from a location they were present at and potentially be linked to a crime scene or event. DNA proved that suspicion correct when it came to prominence in the 1980s. DNA can be extracted from many sources, such as hair, bone, skin, teeth, saliva, semen, and blood. It identifies an individual through our 23 pairs of chromosomes. A chromosome is created by selecting one of the 46 cells each of our parents donate during procreation while the other half of their cell donation is disposed of. The selected cells combine to create our full set of DNA, which is known as a human genome. DNA is unique for each person.

The first trial involving DNA evidence took place in 1986, and the first DNA exoneration occurred in 1989. According to the Innocence Project, DNA evidence has resulted in 375 exonerations to date. Of them, 21 exonerees served time on death row, and 44 pleaded guilty to a crime they did not commit. Some disturbing facts are associated with the exonerations: 69% involved eyewitness misidentification, 43% involved misapplication of forensic evidence, 29% involved false confessions, and 17% involved informants. In the 102 cases that involved false confessions, the real perpetrators were identified in 76 cases, and they went on to commit 48 additional crimes that they were convicted of.

For those exonerees and others who have avoided prosecution as a result of DNA evidence excluding them as the perpetrator of the crime at issue, DNA earned its label as the gold standard in forensic evidence. Yet, what about the cases where DNA is present due to secondary or tertiary transfer, and a conviction ensued?

“The problem is we’re not looking for these things,” said British researcher Peter Hill. “For every miscarriage of justice that is detected, there must be a dozen or more that are never discovered.”

Jennifer Friedman, a Los Angeles based public defender and DNA Specialist agreed. “Although clear cases appear to be quite uncommon, I think it’s probably more prevalent than we think,” she said. “The problem is that what we don’t see frequently is the ability to definitely prove that transfer occurred.”

DNA unquestionably can determine who shed the biological material, but it cannot determine how or when it was transferred to the object it was lifted from. Primary transfer is “the engine that turns the wheels of justice,” said attorney Erin E. Murphy, author of Inside the Cell: The Dark Side of Forensic DNA, and secondary transfer is “the cog that causes the wheel to grind to a halt.”

Secondary Transfer Incidents

In late November 2012, a group of men broke into the home of Silicon Valley multimillionaire Raveesh Kumara. He and his wife were tied up, blindfolded, and gagged. The men robbed the home and fled. Kumara died because the duct tape used as a gag suffocated him. Santa Clara County forensic examiner Tahnee Nelson Mahmet was able to recover enough biological evidence from the gloves, fingernails, and duct tape to conduct DNA testing. She produced three profiles: DeAngelo Austin’s, 22, DNA was on the duct tape; Javier Garcia’s, 21, was on the gloves; and 26-year-old Lukis Anderson’s DNA was on Kumara’s fingernail clippings. They were arrested and charged with murder.

Cellphone tower evidence placed Austin and Javier in the area of the scene, and Austin’s sister revealed she had been in a relationship with Kumara for the previous 12 years and provided her brother with a map of Kumara’s home. The investigation, aside from the DNA, was failing to connect Anderson to the scene. His only other run-ins with the law were a burglary that appeared to be nothing other than breaking a window during a drunken stupor and alcohol-related crimes such as drinking in public and riding a bike while intoxicated.

Anderson told his public defender, Kelly Kulick, that he didn’t do things like the Kumara break-in and murder. “I drink a lot,” Anderson recalled telling Kulick. “Maybe I did it.” Anderson’s medical records were pulled to use as a possible source of mitigating evidence if he faced the death penalty. Those records showed that Anderson was not only drunk on the night of the crime, but at the time of its commission, he was hospitalized under 15-minute watches. A blood test revealed he had consumed the equivalent of 21 beers.

Further investigation revealed that Anderson was picked up off the street by an ambulance crew and transported to the hospital. Coincidentally, it turned out that the same crew responded to the Kumara murder scene and attempted to revive Kumara. They put the same pulse oximeter on Anderson and Kumara’s finger, which is how prosecutors suspect the DNA transferred under Kumara’s fingernails.

After almost six months in jail, Anderson was released. Garcia and Austin were convicted. “The sad thing is, I wouldn’t be surprised if [Anderson] actually pleaded to something,” said Christopher Givens, Garcia’s attorney. “They probably would have offered him a deal, and he would have been scared enough to take it.”

In 2008, DNA had European authorities hot on the trail of the “Phantom of Heilbronn,” a suspected serial killer and burglar of mythical stature who robbed jewelers, burglarized cars, and murdered multiple people, including a law enforcement officer. The Phantom left DNA all over the continent, leaving evidence at 40 crime scenes in Germany, France, and Austria. The Phantom was eventually identified, but she wasn’t an international criminal mastermind. She was an elderly Polish factory worker who unwittingly transferred her DNA to the forensic swabs she was manufacturing, resulting in investigators later transferring her DNA to a slew of unrelated crimes across Europe.

Murphy profiled the horrific 2009 murder of a Yale graduate student who was found dead in a mechanical chase behind a wall in a scientific lab. DNA obtained from the victim’s body and clothing uncovered two unique profiles: one was a coworker in the lab and the other was a local convicted felon.

Of course, the convicted felon was considered the prime suspect. He had intimate knowledge of the mechanical chase because he was a construction worker who had worked behind the wall years earlier. The problem with him being the culprit was that the man died two years before the murder. The secondary transfer of his DNA was attributed to the fact that he shed skin and sweat cells in the area, and it was closed to traffic and adjacent to the tightly controlled laboratory environment.

“The Yale story illustrates how important it is, now that we have the capacity to link perpetrators to an offense by the presence of their DNA in criminal evidence to understand completely how easy it is for such cells to appear in a sample with which the DNA donor has never come into contact,” Murphy wrote in his book. “Absence a solid alibi—in this case, the irrefutable proof of his prior death—the worker might have ended up implicated in the crime. His familiarity with the space, along with his prior record, might have been used against him to prove that he had special knowledge of a good place to dispose of the body.”

It was speculated that the dead man was what researchers refer to as a “good shedder.” David Butler, an English cabdriver, is also a good shedder. He was targeted by investigators after his DNA was found under a victim’s fingernails six years after she was killed. Butler had a severe skin condition that earned him the nickname “Flaky.” Despite a lack of other evidence tying Butler to the crime, prosecutors were not buying his secondary transfer theory that the victim picked up his DNA while riding in his cab. Fortunately for him, a jury did and acquitted him.

“DNA has become the magic bullet for the police,” Butler said. “They thought it was my DNA, ergo it must be me.”

DNA may be considered the gold standard of forensic evidence, but results can vary from lab to lab and analyst to analyst—a fact most people are unaware of. The California Innocence Project commissioned a large private lab to test evidence it believed could exonerate a convicted murder. The lab reported the DNA was inconclusive. So, lawyers took the sample to another analyst, who found the evidence unmistakably cleared the convicted individual.

Mike Semanchik, an attorney with the California Innocence Project, said it would have been a disservice to his client to have not had another analyst look at the evidence. Yet, the implications of differing results troubled him. “How can two labs get entirely different answers from the same DNA tests?” he wondered.

When DNA is the only evidence in the case, “this emphasizes that we need to interpret the entirety of the case,” said Associate Professor Krista Latham, an internationally known anthropologist. “Even everyday people on a jury need to understand that DNA is not this magic bullet, that it needs to be interpreted like any piece of evidence.”

Indirect Transfer Research

“When you consider that over 10,000 cells can fit on the head of a pin, it becomes clear that the days of testing only large, visible stains are long past,” Murphy explained.

“We leave a trail of ourselves everywhere we go. An average person may shed upward of 50 million skin cells a day . . . in two minutes the average person sheds enough skin cells to cover a football field. We also spew saliva, which is packed with DNA. If we stand still and talk for 30 seconds, our DNA may be found more than a yard away. With a forceful sneeze, it might land on a nearby wall,” stated a Wired magazine article titled, “Framed for Murder By His Own DNA.”

Technological advances over the last two decades have enabled DNA to be identified from miniscule amounts of body tissue or fluid. This rapid increase in the sensitivity and discriminatory power of DNA technology has taken us from requiring a large, visible stain to produce a full DNA profile, to where only a single cell can produce the identification result.

This advance in technology has pushed applications of trace DNA, or “touch DNA,” to the forefront. A DNA profile can be created from DNA elicited by contact or natural shedding, from sweating and/or oils secreted from the skin, and trace quantities picked up from saliva. With the increased sensitivity, analysts are provided with samples that contain mixed samples from two or more persons.

The first study to demonstrate that trace amounts of DNA can be transferred from a person to another person or object was published by Roland van Oorschot in a 1997 edition of the science journal, Nature. That revolutionary, and inconvenient for many, idea did not catch on right away, as the scientific community resisted the consideration of secondary or tertiary transfer outside the laboratory or that it was relevant to their work.

“Around the mid-00s, it became more accepted that DNA transfer was an issue that needed to be taken into consideration. And since then, we have even more sensitive technology, so the prevalence of mixed DNA profiles is much, much more frequent,” said Dr. Georgina Meakin, a forensic scientist. “We are in some ways the victims of our own success: we’re getting better and better at detecting DNA, but worse at being able to say, ‘where is the DNA actually coming from, and how did it get there?’”

“When you’re interpreting DNA at a crime scene or from an exhibit within a crime scene, it’s so important to try to establish whether that DNA was deposited directly— that is, by someone who was involved in the crime—or [whether it got there] indirectly,” said Dr. Meakin. Her research and that of others have been focusing on how to make that determination.

Researchers are focusing on understanding the factors and variables that impact the transfer, persistence, prevalence, and recovery of DNA. There are 17 study areas of particular interest to researchers, including the efficiencies of different extraction methods, substrate considerations, environmental conditions, persistence of DNA in various situations, shedder considerations and shedder propensity determination, duration and handling/contact, objects used habitually, accumulation of DNA from multiple contacts, levels of primary user’s DNA on regularly used items, levels of background DNA, and level of profile degradation information.

In addition to determining what type of swabs produce the best samples, researchers are investigating the use of tapes and gels for DNA sampling. As to DNA persistence, researchers have found that DNA left on articles outdoors degrade rapidly, but most samples collected from items kept within indoor environments are less affected and provide good samples for long periods after deposition. DNA profiles have been generated from blood stains and “touch” deposits on skin specimens after several days of being immersed in water. A male consensual partner’s DNA was found to remain under a female’s fingernails after showering. Small deposits of biological material often still provide sufficient DNA to generate full profiles after the items have been hand washed and rinsed but not after cleaning in a dishwasher. Studies also showed sufficient DNA for profiling can be recovered from cuttings of semen stains on polyester fabric after washing, with the amount dependent upon the type of washing.

Another study looked at the level and origins of background DNA on worn upper garments. As expected, the wearer’s DNA was found on internal and external areas of the garment. The DNA of individuals living in the residence or sharing a space was frequently detected on outside areas of the garment. How long a person handles a garment does not appear to affect the amount of DNA deposited, and the person last handling the garment left the most DNA even though they may have only touched it for a few seconds. In one study, a father’s sperm cells were found on a daughter’s underwear as a result of washing clothes together in a washing machine.

One study took samples from single use office spaces that were used temporarily by another occupant for 2.5–7 hours. The regular occupant was the major or majority contributor of DNA on most items while the temporary occupant’s DNA was not found on all items they touched, but their DNA was detected on most items they touched. The researchers also observed profiles from other individuals, including colleagues, family members, and other unknowns as mostly minor contributors.

In sum, conditions affect the possibility of DNA transfer. The rate of transfer varies based upon the “type of biological material and quantity deposited, moisture content of biological material, types of substrate(s) and their properties, contact or lack of contact between involved substrate(s), and when contact is involved, the type of contact and number of transfer event(s) involved,” wrote Devin (Alanah) Thornbury in an academic paper titled “Indirect DNA Transfer Without Contact of Dried Biological Materials” published in Forensic Science International: Genetics.

Thornbury’s research found that “DNA present on personal fabric items can transfer with relatively minimum agitation to a secondary surface without contact.” That conclusion was made after taking items that had biological material, such as dried blood or semen, and holding it above a surface and tapping the fabric item where it was stained. The result was that “[s]ubstantial quantities of DNA were transferred and the resulting profiles from this transferred DNA were generally informative partial of full profiles.”

“There are many possible activities and sources that can be responsible for creating background DNA on items and surfaces, the extent to which DNA collected from a surface can be said to have more likely come from direct contact, indirect contact, or indirectly without contact, will require further investigation,” wrote Thornbury. As the possibility of indirect DNA transfer can occur under various conditions, “this form of transfer must be considered as a possible means for transfer to occur when possible transfer pathways are being assessed during forensic investigation.”

In one of her previous experiments, forensic DNA analyst Cynthia Cale found that when two people shook hands for ten seconds—which is two to five times longer than the normal handshake—and one person picked up a knife, the other person’s DNA was found as a major source of the DNA on the knife one in every 14 times. 

In a separate study conducted by Leann Rizor at the University of Indianapolis in Indiana, four students sat at a table while 12 others watched without sitting at the table. The four at the table pretended to pour drinks from an empty pitcher into empty glasses, touching only their own glasses and the pitcher. The 12 bystanders were allowed to leave the room, talk, and move around. The DNA of students at the table landed not only on their own cups and the pitcher but also on the cups of other students. More importantly, the DNA of the watchers also was found on the swabbed items. Rizzo suspects the watchers’ DNA transferred when they coughed, sneezed, or talked. Researchers could not determine who touched the pitcher last by measuring how much DNA was on the objects. They also could not tell how long someone had touched a pitcher or cup.

One of the key factors in DNA deposition in touch DNA is a person’s shedder status. Shedder status factors have been determined to be based upon interindividual differences such as the sex, age, handedness, and the time period that has passed since the last hand washing.

One study found that individuals who left large deposits of DNA by touch one day may deposit no detectable DNA the next day despite a restriction on hand washing close in time to deposition. In a study where participants wore gloves and used a screwdriver, good shedders deposited more DNA than bad shedders on the outside and inside of the gloves regardless of being the first or second user of the gloves. Researchers also determined that the DNA profile of the first wearer was found on the screwdriver in several instances despite the fact the first wearer never touched the screwdriver, but the levels of DNA in this instance were “generally low and partial profiles. Nevertheless, our results show six out of 19 cases in which the deposited DNA in the break-in tool matched the DNA profile of a person who was never in contact with the tool.”

“We identified the shedder status of an individual as an important factor influencing the extent of primary DNA transfer rather than the order in which the object is handled by different persons,” wrote the authors of the article titled, “Secondary DNA transfer by working gloves,” which appeared in Forensic Science International: Genetics. “In order to prevent innocent people being falsely accused of a crime, an overall comprehension of the possible dimensions of indirect DNA transfer needs to be formed,” the authors warned.

At this point in time, the scientific community cannot determine whether detected DNA may have arisen from a direct contact with an item or through one or more intermediaries. “With the increase of sensitivity [of DNA samples], absence and presence of DNA is not sufficient to discriminate between primary and secondary transfer. DNA results need therefore to be described more precisely in terms of quantity and/or quality to show which extrinsic characteristics help discriminate alleged activities,” wrote the authors of the article titled, “Helping to Distinguish Primary from Secondary transfer events from trace DNA,” which was also published in Forensic Science International: Genetics.

Those authors emphasized two points. “[F]irst, answers to questions regarding activity level propositions are probabilistic in nature and that no experiments will tell us whether transfer was primary or secondary. Following this, whether transfer was primary or secondary is, ultimately, for the Court to consider given all the available information.”

There was no consideration of tertiary transfer in the majority of the research reviewed for this article. One article published in the Australian Journal of Forensic Sciences touched on this type of transfer. It noted that one study found 87.5% of samples provided less than half of the expected material needed for analysis. In another study, 17% of samples were of enough quality to be reported and go through a database in search of a profile.

Researchers are exploring ways to assist courts and juries in determining the probability of direct or indirect DNA transfer.  Bayesian Network is the leading probabilistic model being used to define the relationship between variables and to calculate probabilities of a DNA sample being the result of direct or indirect transfer.  Bayesian Networks allow visualization of the structure of the model, provides insight into the presence and absence of the relationships between random variables, and provides a way to research the issue of indirect DNA transfer.

The leader in research on indirect DNA transfer is Australia. The U.S. is lagging on indirect DNA transfer research, and U.S. researchers incurred a black mark with the publication of the paper published on August 1, 2018, in Forensic Science International: Genetics titled, “NIST inter laboratory studies involving DNA mixtures (MIX05 and Mix13): Variation observed a lesson learned.” That paper found two-person DNA mixtures at four different mock sexual assault scenes. Shamefully, the authors not only tried to prevent their findings from being published for peer review, they inserted language that could potentially lead to it not being introduced as evidence in U.S. criminal case. [See: CLN, Oct. 2019]

“I first learned about the results of this study in 2014, at a talk by one of its authors. It was clear that crime labs were making mistakes, and I expected the results to be published quickly,” wrote Greg Hampkin, a biology professor at Boise State University and founder of the Idaho Innocence Project in a New York Times article. “Peer-reviewed publication is important because most judges won’t let you cite someone’s PowerPoint slide in your testimony. But years went by before the study was published, preventing lawyers from using the findings in court, and academics from citing the results in journal articles. If some of us had not complained publicly, it may not ever have been published.”

The latest law enforcement move in DNA is rapid analysis. The Rapid DNA Act of 2017 authorized the FBI to “issue standards and procedures for the use of Rapid DNA instruments and resulting DNA analyses.” The FBI has not authorized rapid analysis machines to process crime scene DNA because that process destroys or consumes the sample, which prevents further testing. Therefore, the FBI only allows Rapid DNA instruments to process buccal (mouth) swabs taken from arrestees to be loaded into its Combined DNA index System (“CODIS”). According to the FBI, 85-90% of the time Rapid DNA machines produce full CODIS eligible DNA profiles from buccal swabs. “ However, reporting indicates that some state and local law enforcement agencies have used Rapid DNA instruments to analyze crime scene samples and to compare profiles in [State DNA Index Stysems] and [Local DNA Index Systems],” the Congressional Research Service wrote in an April 2022 report.

Rapid DNA instruments work well on “single-source DNA” or DNA that comes from a single source. Problems arise when the sample has a mixture of DNA from more than one source. In those cases, a forensic scientist is needed.

“Mixture interpretation is the most difficult thing that crime laboratory analysts have to do by far,” said Vincent A. Figarelli, superintendent of Arizona’s Crime Laboratory System.  “There is no way you want a Rapid DNA operator doing a mixture analysis.”

DNA Databases, Genealogy, and Face Rendering

As of October 2021, more than 200 labs in the U.S. participate in the National DNA Index System (“NDIS”), and the database includes nearly 15 million offender profiles, more than four million arrestee profiles, and more than one million forensic profiles. CODIS searches across those indexes for potential matches or hits. “No names or other personal identifiers for offender and arrestee DNA profiles are stored in the NDIS, so when a match is made in CODIS, the laboratories that submitted the DNA profiles to the NDIS are notified of the match and they can contact each other to verify the match and coordinate their efforts,” wrote the Congressional Research Service. These databases are restricted to law enforcement use.

Genealogists have used DNA to help people trace their roots. and 23andMe are the two largest public genealogy websites, but other sites such as GEDMatch and FamilyTreeDNA also help users learn information about their relatives. People who use these services upload their DNA into a database to obtain a match to locate a relative on their family tree. These databases, however, also have been used to solve crimes. Most require an opt-in for a profile to be used by law enforcement.

Genetic genealogy has uses beyond law enforcement and to satisfy curiosity; it has been used to discriminate. In northwest China, officials have been using genetic ancestry since July 2017 to identify members of the Uyghur minority group by collecting iris scans, fingerprints, and DNA from everyone between the ages of 12 and 65 in the Xinjiang Uyghur Autonomous Region.

“When you give any authority such important information and such strong leverage against individuals, you start to worry very, very much about the shape society’s going to take,” said Yves Moreau, a biologist and engineer at the Catholic University of Leuven in Belgium. “You put people in a database because you want to control them.”

In April 2018, California law enforcement officials used genetic genealogy to identify Joseph James DeAngelo, Jr., a former police officer, as the notorious Golden State Killer. The public was widely acceptive of that method, and it spurred CeCe Moore, the most prominent figure in the field of genetic genealogy, to ally her techniques to solving crimes. Moore teamed up with Virginia-based Parabon NanoLabs to solve the 1980 rape and murder of Barbara Tucker. They used profiles on GEDMatch to isolate Robert Plympton as the suspect. In other words, a family member he may have never met submitted a DNA sample that led law enforcement to Plympton’s doorstep. Law enforcement as far back as 1987 had loaded DNA taken from semen at the scene into CODIS, but they did not come up with a match then or when making later inquiries for a match.

Parabon NanoLabs has taken DNA to a controversial new level by using a DNA sample to create a face sketch. This is known as phenotyping, and it uses coding genes to predict what a person may look like based  on their DNA. Genes are broken down onto coding and non-coding genes. There are different variations of any gene, such as genes for blue eyes or brown eyes, and these variants are called alleles. Coding genes make up a little more than 1% of the human genome.

When it was just a fledgling company in 2011, Parabon applied for and was awarded a U.S. Department of Defense (“DoD”) grant to try to reconstruct a person’s appearance from their DNA. The DoD wanted to develop the technology, so it could identify the makers of improvised explosive devices from the miniscule amounts of DNA left on bombs, but it also knew law enforcement would be interested. Parabon succeeded by collecting a large number of DNA samples and face photographs and then training algorithms to pick out relationships. The company says that since 2018 it has helped police solve more than 120 cases with the help of their genetic genealogy and phenotyping methods.

Scientists have published hundreds of papers on the relationship between specific genetic variants and physical features, says Manfred Keyser, a researcher at Erasmus University Medical Center in Rotterdam, but they still don’t know how these individual traits become a unique human face. “It’s very limited, what we know about the face, and this particular company says they can predict it from DNA,” said Keyser. “It’s pretty bad that they don’t publish how they do it and how they validated this.”

Accepting Indirect Transfer as Real Evidence.

“It requires a lot of investigation to identify where that person [whose DNA profile was found] was,” said Dr. Meakin. “It’s a little like COVID-19 contact tracing where they’re working out how the virus has travelled between people.”

Despite those difficulties and DNA’s reputation as the gold standard of forensic evidence, Canadian Courts are being very careful in scrutinizing DNA evidence, especially in circumstantial evidence cases. Those courts have said that DNA evidence found on an object is “powerful evidence” that a person touched the object, but “the connection of the accused with the crime will depend on the existence of other evidence capable of establishing . . . contact with the object at the relevant time and place.” R v. Grayston, 2016 ONCA 784.

In R v. Sabrie, 2017 ONCA 6134, a swab was taken from a complainant’s breast that contained the accused’s DNA. The Court found enough evidence was not submitted to rebut the possibility of secondary transfer. “I am also mindful that Mrs. Shacker was qualified as an expert in the comparison and analysis of DNA. She was not qualified as an expert in the transference of DNA,” the trial judge found. “It is critical that an expert be confined to giving evidence only in those areas that they have been properly qualified. I find that Ms. Shacker’s evidence about transference was outside her area of expertise and as such impacts the amount of weight I am prepared to place upon it.”

In another case, the ONCA overturned the conviction in a break and enter case and ordered acquittal. It found the Crown had “called no expert evidence on the characteristic of DNA evidence or how it may be transferred,” or whether the “appellant’s DNA was the sole profile on the glove.” R v. Donoghue, 2019 ONCA 534. The Court confirmed that “presence of the accused’s DNA is not determinative of guilt and does not lead inexorably to only one inference such as to support a conviction at trial.”

Courts in the U.S. would be well advised to take note of how Canadian courts treat DNA evidence and the very real and important issue of secondary DNA transfer.

A consensus is building that secondary and tertiary transfer of DNA occurs and that it can, and has, led to individuals being accused and convicted of crimes they did not commit. At a March 13, 2021, conference for English public defenders, Judge Andrew Heasler presented a paper that gave a stern charge to the medicolegal system to be aware of this phenomenon. “The science community can take the credit for the ‘gold standard’ appellation often given to DNA evidence, but, and it’s an important but, every forensic scientist and legal practitioner must ensure that the over enthusiastic use, or misapplication of, DNA evidence does not result in miscarriages of justice and the consequent devaluation of this important investigative and evidentiary tool.”

The U.S. criminal justice system has been alarmingly slow to accept secondary and tertiary transfer, says Kelley Kulick, a public defender in Santa Clara County, California, who was Lukis Anderson’s lawyer and obtained an acquittal in another case after proving secondary transfer. “It rattled what we believe is the gold standard. We like certainty and when suddenly DNA can’t be relied upon, people don’t like that,” Kulick said.  

Sources:,,,,,,,, Wired,,,, Forensic Sciences International: Genetics,,,,, MDPI, Australian Journal of Forensic Sciences, La Trobe University School of Life Sciences; Master’s Thesis Devon (Alanah) Thornbury, Congressional Research Service.

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