Miriam Aroni Krinsky, executive director of Fair and Just Prosecution, and Rebecca Blair, senior research associate at Fair and Just Prosecution opine for NBC News:
Last week, police announced they had arrested
Bryan Kohberger in the brutal murders of four
University of Idaho students. After a weekslong investigation, authorities
zeroed in on Kohberger in part by comparing DNA
found at the crime scene with DNA of a relative of Kohberger
apparently obtained from the family’s home trash.
With only limited information available, it is far
too early to judge the strength of the prosecution’s case. But the role DNA has
already played has drawn renewed
attention to broader issues around the uses and limits of this
technology — and scientific evidence more generally — in the criminal legal
system.
At its best, DNA testing can tell you whose genes
were found in a particular location — but it can’t tell you how they got there.
The approach used to identify Kohberger is just one
of several recent developments in DNA analysis that have transformed the way
law enforcement investigates crimes. While these advancements present
tremendous potential for law enforcement and criminal investigations, burgeoning
new areas of forensic analysis also have shortcomings that underscore the need
to proceed with caution and recognize that not all technological advancements
are foolproof.
Over the past decade, recognition of the deep flaws in
many common forensic techniques — like blood
spatter, hair or bite
mark analysis — has grown, even as pop culture continues
to depict often-questionable forensic methods as infallible
determinants of scientific truth.
In a justice system rife with flawed science, DNA
evidence is rightly viewed as the gold standard for forensics: After DNA
evidence was first introduced in the criminal justice system in the late 1980s,
scientists spent years developing
and evaluating protocols for comparing individual DNA samples, which
have been repeatedly found to produce consistent, reliable results.
This has enabled investigators to crack decades-old cold cases and
contributed to the exonerations of at least 568
innocent people. But while the value of DNA analysis in criminal
investigations is now widely recognized, the limits and pitfalls of DNA testing
technology and other often less credible sciences are not sufficiently
understood among prosecutors, law enforcement and the public.
DNA analysis was a revolution in forensics, but like
every form of scientific evidence it has the potential for error. At its best,
DNA testing can tell you whose genes were found in a particular location — but
it can’t tell you how they got there. An innocent
person’s DNA might be found at a crime scene because they brushed
against the victim on the street, used the same doorknob as the perpetrator or
dropped a cigarette butt nearby.
Recent technological advancements allowing
scientists to analyze increasingly small or contaminated DNA samples further
complicate the process. While these new techniques can yield valuable insights,
they require more subjective judgment and thus are far more
likely to produce false
matches than traditional testing. DNA samples are also sometimes
mishandled or tampered with, compromising results.
DNA often yields powerful insights, in particular
when used in ruling out individuals: Analysts can identify
inconsistencies between two DNA samples that make it nearly impossible
for both samples to have come from the same person. But because the DNA of any
two people is more than 99%
identical, it is far harder to say with total certainty that two DNA
samples must have come from the same person, particularly when
dealing with incomplete or tainted samples.
And while the absence of a suspect’s DNA from the
crime scene can, in some cases, provide strong evidence that they were not
present or implicate another suspect, the presence of their DNA is not always
evidence of guilt. As such, reliance on DNA alone in investigations, absent
other corroborating facts, can lead to tunnel
vision and confirmation
bias, in which law enforcement and prosecutors subconsciously discount
evidence that points away from their chosen suspect.
To guard against mistakes, law enforcement and
forensic scientists must set strict protocols for collecting and handling
genetic material to ensure samples aren’t contaminated or degraded. Prosecutors
should be educated on the developments in, and limitations of, DNA analysis and
other forensic techniques, and defense attorneys should always be provided with
equal access to evidence and testing, allowing them to probe potential errors.
Furthermore, forensic evidence should rarely, if ever, be the sole basis for
arrest or prosecution — and the public should keep that in mind as it absorbs
information in high-profile cases involving DNA.
Bryan Kohberger looks toward his attorney, public
defender Anne Taylor, right, during a hearing in Latah County District Court on
Jan. 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 the perpetrators — raises additional concerns. While
promising in its ability to help solve cases, the technique has enabled law
enforcement to gain access to the DNA of nonsuspects.
Furthermore, misuse of this information could carry
profound consequences, and it’s crucial that we protect against abuses.
Because Black and
Hispanic people are significantly
overrepresented in law enforcement databases, they are also
disproportionately likely to be implicated by
this genealogical analysis, potentially exacerbating 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 present
immediate public safety risks. It also requires that law enforcement obtain informed
consent before analyzing the DNA of nonsuspects (like family members), unless
doing so would compromise the investigation.
The protections in the Maryland law should be
replicated nationwide, especially as we continue to see law enforcement agencies
exploit private health information — like DNA collected from newborn
genetic screenings or examinations
of rape victims — to identify crime suspects.
We also need protections against misuse of other
forensic advancements. To that end, district attorneys should have a point
person on forensics within their offices who is versed on these issues, and
advocate for state forensics science commissions (like that created in
Texas) to ensure that discredited sciences don’t form the basis for
arrests, prosecutions and convictions.
We will have to wait to find out what the
investigation into the unthinkable murders of four Idaho students ultimately
yields. But while we struggle to confront the senseless horror of these
killings, and commend the efforts of law enforcement to solve the case, we
should also remember that each high-profile incident presents an opportunity to
push for better, more rigorous standards. Victims and survivors of crime and
the broader community, as well as individuals charged and arrested, deserve no
less.
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