Caution: DNA may incriminate the innocent

In December 2012, a homeless man named Lukis Anderson was charged with the murder of Silicon Valley multimillionaire Ravish Kumra, based on DNA evidence. Had he been convicted, Anderson would have faced the death penalty. But Anderson was innocent. And he had a solid alibi: on the night of the murder, which happened in November of that year, Anderson was admitted to the hospital drunk and almost unconscious and was under continuous medical supervision throughout the night. At a later stage, the defense team representing Anderson learned that his DNA had arrived at the crime scene through the paramedics who were called to Kumara's home. Earlier that day, the paramedics treated Anderson, and without their knowledge "planted" the suspicious evidence at the crime scene that happened more than three hours later. The case, which was presented in February 2016 at the annual conference of the American Academy of Forensic Science in Las Vegas, is a clear example of the criminalization of an innocent person due to the random transfer of DNA to a crime scene. Following this case and other similar cases, there are more and more voices calling for the criminal justice system, which sometimes relies too close to DNA as certain evidence, to change attitude and recognize the inherent danger of distorting the law.

Since almost all forensic identification methods have come under severe scientific criticism in recent years, especially comparative methods, for example, of bite marks or microscopic analysis of hairs, the power of DNA evidence has increased, and not for nothing. DNA analysis provides more absolute and less subjective results from other forensic methods, since it is based on statistical models. Examining specific regions or gene sites in the human genome allows researchers to determine the likelihood that any evidence matches or does not match a known genetic profile of a crime victim, crime suspect, or alleged offender. Moreover, by examining the prevalence of a particular genetic pattern in population databases, researchers can predict how well-founded and evidential the match is. Since the mid-90s, a non-profit legal organization has been operating in New York The Innocence Project The effort to vindicate the innocent who were convicted for no wrongdoing. The organization is again conducting analyzes of available DNA samples to test the validity of convictions, and so far has managed to obtain about 200 convictions and mobilize widespread public support in calling for reform of the US criminal justice system.

However, like any forensic evidence, DNA is only part of a larger picture. "We hope with all our hearts that DNA will save the day, but the problem is that the whole system is fundamentally flawed," says Irene E. Murphy, a law professor at New York University and author the book Inside the Cell: The Dark Side of Forensic DNA, which was published in 2015 [dealing with the dark side of using DNA as forensic evidence]. "If the method is applied sweepingly, without proper skepticism and consideration, the distortion of the law is inevitable." For example, biological samples may deteriorate over time or become contaminated Judges and juries can misinterpret statistical probabilities, and as Anderson's case shows, skin cells can move from place to place.

In 1997, researchers proved for the first time that it is possible to extract genetic information about a person based on skin cells he left behind on some object. Since then, this type of evidence based on traces found at a crime scene, also known as touch DNA, is increasingly used in forensics, and such DNA samples are routinely collected from surfaces such as doorknobs or gun butts. (2009 times between 2013 and XNUMX, and this is often done to locate suspects in property crimes such as theft, robbery, or burglary.) Commercial companies are currently selling law enforcement agencies kits that allow the production of a complete genetic profile of a person based on a sample of single skin cells, sometimes Only three to five cells. Even independent laboratories and scientists engaged in, for example, identifying bodies found long after death use these kits.

Until recently, DNA samples of this type were considered conclusive proof of direct contact. But studies are increasing that show that DNA does not always remain at the place of contact. For example, a person who carries with him a handkerchief that was used to wipe another person's neck, can carry that person's DNA and transfer it to some object that the other person has never touched. This is reported by a study published in early 2016 in the International Journal of Forensic Medicine. A similar scenario describes Cynthia M. Kyle, a graduate student in human biology at the University of Indianapolis, in a recent article published in the Journal of Forensic Science, details a case of a man who used a steak knife and transferred another man's DNA to the handle of the knife after shaking his hand. In fact, in a fifth of the cases studied by Kyle, it turned out that the person identified as the primary source of the DNA sample had never touched the knife. Kyle and her colleagues' research team is just one of several teams working to measure how easily skin cells move from one place to another and how long they stay there. "What you find at the crime scene is what's there," says Kyle, "but the question is how the genetic profile is used and how it is presented in court, and here we have to be careful."

At the American Academy of Forensic Science conference held in Las Vegas, Kelly Kulik, the representative of the public defender's office in Santa Clara County, California, hypothesized that Anderson's DNA traces were transferred to the murder scene on the uniforms of the paramedics who treated him. So far, it is not known how common the cases are Transferring DNA from scene to scene leads to a wrongful conviction. "True, clear cases of wrongful conviction seem to be quite rare, but in my opinion the phenomenon is more common than it is common to think," says Jennifer Friedman, an attorney with the Los Angeles Public Defender's Office and an expert in DNA evidence. "The problem is that there is not often We have the possibility to prove beyond any doubt that the transfer of DNA did take place."

The misinterpretation of the DNA sample in Anderson's case was a contentious issue in the trial of the two defendants now on trial in the Kumara murder, Kulik says. There is no doubt that DNA evidence is still a valuable tool in criminal investigations, but both forensics and legal experts emphasize that additional supporting factual evidence is needed to establish guilt or innocence. Like any other piece of evidence, DNA provides only one circumstantial clue in the investigation of a crime mystery. And so Anderson's case serves as a warning against asking us to draw fates based on just a few stray skin cells.