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Cynthia Cale (left), pursing a master's degree in Human Biology  at the University of Indianapolis , designed and conducted the secondary DNA transfer study with fellow student Madison Earll (not pictured), who has since earned her degree. They worked under the guidance of Associate Professor Krista Latham (right).Touch DNA can be transferred by a handshake from one person to another, then to an object like a knife or a gun. But new research has found that Touch DNA analysis can erroneously implicate a person who never even laid eyes on the weapon as the main contributor of the DNA on its handle. 

The startling finding, reached by University of Indianapolis scientists, means that the invisible traces we may be leaving everywhere we go – scientists don’t yet understand the minute mechanics at work – could be affecting current and future cases. But how far back the traces could affect past verdicts, and sentences, has yet to be determined.

The results won’t cause a wholesale reevaluation of criminal convictions, contends Cynthia Cale, the lead author of the study forthcoming in the January issue of the Journal of Forensic Science.

Cale told Forensic Magazine that now is a crucial time to begin understanding how touch DNA needs to be interpreted and analyzed – not just by forensic analysts, but also by prosecutors and defense attorneys. The new technology means we have to relearn how to think about DNA, she said in the phone interview.

“With the increased sensitivity, we’re going to be detecting more DNA regardless,” Cale said. “It could be any DNA left on that object, and it’s going to cause interpretation to be more complicated. I don’t think it’s calling into question old cases – it’s now and into the future,” she added.

Cale’s experiments began with a two-minute handshake between two people then handling a knife led to the DNA profile of the person who never touched the weapon being identified on the swab of the weapon handle in 85 percent of the samples, according to a new study by University of Indianapolis researchers, entitled “Could Secondary DNA Transfer Falsely Place Someone at the Scene of a Crime?”
In one-fifth of those experiments, the person who had never directly touched the knife was identified as the main or only contributor of the DNA on the handle, according to the study.
Cale called the results potentially “scary,” in a school statement announcing the results.

Previous work had established the possibility of transferring DNA before. As early as 2002, the possibility was mentioned by a group of researchers in the United Kingdom. However, the results have not always appeared to be consistent, since it appears the capacity to “shed” DNA is different from person to person, and can even change at different times for different people. A 2007 study in New Zealand, for instance, found that the phenomenon of “good shedders” was relatively insignificant. But only a handful of studies have looked at the possibilities.

“It’s something that’s been mentioned before, but it gets lost in the mix. This could possibly be a concern for us in the future,” Cale said.

Now that DNA-testing is more sensitive than ever before, looking at the possibilities are crucial, she added.

“Every couple years a new article would come out about secondary DNA transfer. For the most part they would say, it could happen, but it’s not going to impact casework in any great capacity. But the tools are increasing sensitivity. I wanted to revisit the issue with current kits… to see if we might have problems in the future.”

Although the sensitivity of the DNA kits has only recently reached the point where the minute traces can be detected, the potential that it could affect verdicts and sentences stretches back nearly a decade, according to Lawrence Kobilinsky, a professor of forensic science and chair of the Department of Sciences at John Jay College.

The Office of the Chief Medical Examiner in New York City has been using high-sensitivity of testing in all five boroughs since January 2006 – and he himself has consulted on cases where secondary transfer could change a previous outcome, Kobilinsky said.

“I believe that this (study) constitutes new information and may be used to overturn a conviction and open the door to a new trial,” the John Jay forensics expert told Forensic. “I think that the present findings may not only impact current and future cases but may also impact previous cases where convictions were obtained based on finding the defendant’s DNA on a weapon.
“I see this as an important issue for labs performing low copy number testing of casework,” Kobilinsky added.

One particular case in Californa made healdines. A man spent months in prison on a murder charge before it was proven that he was hospitalized and so drunk he was incapacitated at the time of the killing. It was later discovered that the same first responders who had treated him and transported him for medical attention shortly afterward responded to the crime scene.

The initial reasoning behind the study was to examine whether first-responders or crime-scene investigators could transfer their DNA to a place where it could contaminate evidence, Cale said. But it appeared the results indicated that it could even implicate unrelated people who just happened to leave their DNA on another person or an object that could become a point of investigative interest.

Cale said analyzing the science – and the understanding of untold variables still not understood – is paramount.

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