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Idaho murder DNA evidence helps police. But is it infallible?

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Last week, police announced they had arrested Bryan Kohberger in the brutal murders of four University of Idaho students. After a week-long investigation, authorities focused on Kohberger in part by comparing DNA found at the crime scene with DNA from a relative of Kohberger apparently obtained from the family’s household trash.

With only limited information available, it is far too early to judge the strength of the prosecution case. But the role that DNA has already played has drawn renewed attention to broader questions about the uses and limits of this technology — and scientific evidence more generally — in the criminal justice system.

At best, DNA tests can tell you which genes were found in a particular place, but they cannot tell you how they got there.

The approach used to identify Kohberger is just one of many recent developments in DNA analysis that have transformed the way law enforcement investigates crimes. While these advances hold enormous potential for law enforcement and criminal investigation, the burgeoning new fields of forensic analysis also present gaps that underscore the need to proceed with caution and recognize that all technological advances are not infallible.

Over the past decade, recognition of the deep flaws in many common forensic techniques — like analyzing blood spatter, hair, or bite marks — has grown, even as pop culture continues to portray forensic methods often questionable as infallible determinants of scientific truth.

In a justice system plagued by flawed science, DNA evidence is rightly considered the gold standard of forensics: after DNA evidence was first introduced into the criminal justice system in the In the late 1980s, scientists spent years developing and evaluating protocols for comparing individual DNA samples, which were repeatedly shown to produce consistent and reliable results.

This allowed investigators to solve decades-old cold cases and helped exonerate at least 568 innocent people. But while the value of DNA analysis in criminal investigations is now widely recognized, the limitations and pitfalls of DNA testing technology and other often less credible science are not sufficiently understood among prosecutors, law enforcement order and the public.

The criminal justice system is increasingly relying on new and innovative techniques for the analysis of genetic material. As such, it is important that we develop a better understanding, both in the criminal justice field and in the public, of how DNA is used, what it can definitively tell us, and what he cannot tell us. This is especially critical in high-profile cases in which pre-trial publicity of purportedly definitive “scientific findings” can harden thinking and deprive defendants of their right to a fair and impartial jury.

DNA analysis has been a revolution in forensics, but like any form of scientific evidence, it has the potential for error. At best, DNA tests can tell you which genes were found in a particular place, but they can’t tell you How? ‘Or’ What they got there. An innocent person’s DNA can be found at a crime scene because they brushed past the victim on the street, used the same doorknob as the attacker, or dropped a cigarette butt nearby.

Recent advances in technology allowing scientists to analyze smaller and smaller or contaminated DNA samples further complicate the process. Although these new techniques can provide valuable information, they require more subjective judgment and are therefore much more likely to produce false matches than traditional tests. DNA samples are also sometimes mishandled or tampered with, compromising results.

DNA often yields powerful information, especially when used to rule out individuals: analysts can identify inconsistencies between two DNA samples that make it almost impossible that the two samples are from the same person. But since two people’s DNA is more than 99% identical, it’s much harder to say with complete certainty than two DNA samples. must have come from the same person, especially in the case of incomplete or contaminated samples.

And while the absence of a suspect’s DNA from the crime scene may, in some cases, provide strong evidence that he was not present or implicate another suspect, the presence of his DNA does not is not always proof of guilt. As such, reliance on DNA alone in investigations, in the absence of other corroborating facts, can lead to tunnel vision and confirmation bias, in which law enforcement and prosecutors unknowingly ignore evidence that strays from the chosen suspect.

To guard against errors, law enforcement and medical examiners should establish strict protocols for collecting and handling genetic material to ensure that samples are not contaminated or degraded. Prosecutors should be made aware of the developments and limitations of DNA analysis and other forensic techniques, and defense attorneys should always be given equal access to evidence and testing, allowing them to probe errors potential. Moreover, forensic evidence should rarely, if ever, be the sole basis for an arrest or prosecution – and the public should keep this in mind as they absorb information in high-profile cases involving DNA.

Image: Bryan Kohberger looks toward his attorney, public defender Anne Taylor, right, during a hearing in Latah County District Court on January 5, 2023 in Moscow, Idaho.
Bryan Kohberger looks toward his attorney, public defender Anne Taylor, right, during a hearing in Latah County District Court January 5 in Moscow, Idaho.Ted S. Warren/Pool via Getty Images

The growing use of forensic genetic genealogy – the practice of comparing crime scene DNA with existing DNA databases to identify close relatives of perpetrators – raises additional concerns. Although promising in its ability to help solve cases, the technique has allowed law enforcement to gain access to the DNA of non-suspects.

Additionally, the misuse of this information could have far-reaching consequences, and it is crucial that we protect ourselves against misuse. Since blacks and Hispanics are significantly overrepresented in law enforcement databases, they are also disproportionately likely to be implicated by this genealogical analysis, which can exacerbate racial disparities throughout the system. .

In 2021, the Innocence Project worked with Maryland lawmakers to address these risks by passing the first law regulating the use of forensic genetic genealogy. The bill limits the use of these techniques to only the most serious violent crimes or cases that pose immediate risks to public safety. It also requires law enforcement to obtain informed consent before analyzing the DNA of non-suspects (such as family members), unless doing so would compromise the investigation.

Maryland’s law protections should be replicated nationwide, especially as we continue to see law enforcement agencies exploit private health information — like DNA gathered from genetic tests. in newborns or examinations of rape victims – to identify crime suspects.

We also need protections against the misuse of other forensic advances. To this end, district attorneys should have a forensic pathology reference person within their offices who is knowledgeable about these issues and advocate for state forensic scientific commissions (such as the one created in Texas) to ensure that discredited science is not the basis for arrests. , prosecutions and convictions.

We’ll have to wait and see what the investigation into the unthinkable murders of four Idaho college students ultimately yields. But as we struggle to come to terms with the senseless horror of these murders and salute the efforts of law enforcement to solve the case, we must also remember that every high-profile incident provides an opportunity to apply pressure. for better and more rigorous standards. Victims and survivors of crime and the wider community, as well as those charged and arrested, deserve nothing less.

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