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Super-Sensitive Techniques Make DNA Evidence Lie Sometimes, Expert Says

by Maggie Fox /  / Updated 

Three Myths About DNA


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A 2013 murder case shows just how dangerous it can be to rely on DNA evidence, an expert said Wednesday.

DNA found under the fingernails of murdered California millionaire Raveesh Kumra led police to Lukis Anderson of San Jose. But after Anderson spent five months in jail, investigators found out that Anderson, a homeless alcoholic, had in fact been drunk and passed out in a hospital at the time of the attack.

Image: Houston Forensic Science Center
Forensic analyst Karen Gincoo checks a tray of evidence vials from rape kits in the biology lab at the Houston Forensic Science Center in Houston on Thursday, April 2, 2015.Pat Sullivan / AP

He couldn’t have committed the murder. But investigators discovered that two paramedics who had picked up and moved Anderson also responded to the Kumra murder scene.

Police determined that DNA from Anderson somehow got transferred to Kumra’s body by the paramedics.

Three Myths About DNA


It’s a perfect example of how modern, ultra-sensitive DNA techniques can lead police, judges and juries astray, says Cynthia Cale, a DNA analyst of both the University of Indianapolis and Strand Diagnostics.

“Research done by me and others at the University of Indianapolis in Indiana has highlighted how unreliable this kind of evidence can be,” Cale writes in a letter to the journal Nature.

“We have found that it is relatively straightforward for an innocent person’s DNA to be inadvertently transferred to surfaces that he or she has never come into contact with. This could place people at crime scenes that they had never visited or link them to weapons they had never handled,” she added.

“We asked pairs of people to shake hands for two minutes and then each individual handled a separate knife. In 85 percent of cases, the DNA of the other person was transferred to the knife and profiled. In one-fifth of the samples, the DNA analysis identified this other person as the main or only contributor of DNA to the ‘weapon’.”

DNA evidence once had to be taken from bodily fluids or fairly large bits of tissue. New technology means very small amounts can be picked up and amplified in a lab to get a reading, Cale noted.

“These subtleties are not usually explained in court. Instead, a jury is told that there is a one-in-a-quadrillion chance that the evidence retrieved from the crime scene did not come from a defendant. Naturally, the jurors assume that the defendant must have been there,” Cale wrote.

“We urgently need to review how DNA evidence is assessed, viewed and described.”

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