BU Today

Science & Tech

Not Guilty, Probably

Crime labs need new tools to help interpret mixed and degraded DNA crime scene evidence. A team of BU forensic scientists is on the case.

In 2010 Boise State University forensic biologist Greg Hampikian was contacted by the lawyer for Kerry Robinson, who is serving 20 years in prison after being convicted in 2002 of raping a woman in Moultrie, a small town in southern Georgia. The woman, who was raped by three men, identified only one of her attackers, a man named Tyrone White, and DNA analysis provided what court records called “essentially a conclusive match.”

As part of a plea bargain to reduce his sentence, White named Robinson as one of the rapists. But Robinson’s genetic variations—key markers used to identify the person the DNA belongs to—were such a poor match that as one forensic expert testified, up to 1,000 people among the 15,000 in Moultrie County could likely match the crime scene evidence to the same degree. Still, combined with White’s testimony, the prosecution was able to use the DNA evidence to convince a jury to convict Robinson.

Convictions like Robinson’s happen in large part because of the powerful influence DNA evidence has on a jury, and because of difficulties inherent in DNA analysis, particularly in cases involving multiple suspects and degraded samples.

When Hampikian and another forensic researcher sent the data from the trial evidence—a cheek swab from Robinson and DNA from the crime scene—to 17 accredited crime labs, only one agreed with the lab used by prosecutors. That lab had found that Robinson’s DNA shared some common genetic markers with the crime-scene evidence, meaning that he “could not be excluded” as a suspect. Of the other labs, 4 couldn’t conclude anything from the evidence, and 12 reported that Robinson should be excluded as a suspect. It’s important to note that these labs didn’t find differing numbers of shared genetic variations in the evidence. They just interpreted the strength of that evidence differently, and it’s the interpretation that matters in court.

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