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As Forensic Analysis Techniques Improve, Experts Spotlight Risks of Secondary DNA Transference


By Andrew Z. Giacalone

Lukis Anderson had no idea why he was sitting in a California jail awaiting trial for a crime he was adamant he didn’t commit. According to prosecutors, Anderson’s DNA had been found under the fingernails of murdered San Jose millionaire Raveesh Kumra. That, they said, was enough to put Anderson at the scene of the crime.

But as Anderson maintained his innocence, he also presented a compelling alibi. He could not have possibly committed the crime, his defense attorneys argued, because at the time Kumra was murdered, Anderson was being treated at the Santa Clara Valley Medical Center after passing out drunk in downtown San Jose with blood alcohol levels at five times the legal limit.

However, despite the alibi, the question still remained: how did Anderson’s DNA end up on Kumra? In a news article from 2013, the

San Francisco Chronicle


reported

how prosecutors would soon discover that the same two paramedics who had treated Anderson for intoxication had responded to Kumra’s home just hours later. The traces of Anderson’s DNA had been transferred through them and unwittingly deposited under Kumra’s fingernails.

“Anderson is fortunate that he was at the hospital,” the California Innocence Project

mused

in a blog post. “If he had not been so intoxicated or remained at the hospital, Anderson could have very well have been another wrongful conviction.”

Cynthia M. Cale, a human-biology graduate student at the University of Indianapolis, Indiana and co-author of a recent

study

into the risks posed by secondary DNA transfer, says Lukis Anderson’s case only further demonstrates that the way DNA evidence is assessed and interpreted by law enforcement officials must be reviewed as technological advancements steadily boost the power of techniques available to modern forensic scientists.

In an October 28 article for the weekly science journal


Nature


, Cale warns that it is, in fact, “relatively straightforward for an innocent person’s DNA to be inadvertently transferred to surfaces that he or she has never come into contact with.”

To prove this point, Cale and her team undertook an experiment to show how easily DNA can be transferred from one object to another. They asked pairs of people to shake hands for two minutes and then directed each of them to handle a separate knife. In 85% of the cases, the researchers discovered, the DNA of the other person was transferred to the knife and profiled. In one-fifth of the samples, the DNA analysis identified the secondary person as the main or only contributor of DNA to the potential weapon.

What, asks Cale, can one conclude from the experiment?

“At the very least, the results highlight again that samples at crime scenes must be gathered with great care,” she says, adding that even “apparently rigorous evidence such as DNA profiles can be interpreted in multiple ways, some of which will be incorrect.”

Kareem Belt, a forensic policy analyst at the Innocence Project agrees, noting that with the increased sensitivity of newer DNA kits the chance for secondary and even tertiary transfer becomes “that much more of a possibility since more DNA is being detected.”   

“The DNA laboratory is only going to look at the evidence that’s presented.  It’s incumbent upon law enforcement to build an entire case and investigate as many avenues as possible,” he continues. “DNA should ultimately be used as an investigatory tool that adds to a solid case built on multiple pieces of solid evidence, and not as an immediate indictment when there’s a matching profile.”

Read the entire

Nature

article

here

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