Touch DNA Might Be Contaminating Crime Scene Evidence

DNA has undoubtedly been a breakthrough for modern criminal investigation. It has freed the innocent, solved decades-old cold cases, and given detectives a kind of molecular witness in many cases that may have otherwise remained unsolved.

Except better and more-sensitive technology means more potential problems, in some cases. Mixes of DNA, and the “1-in-X” probabilities are currently being evaluated by some crime labs.

But the latest reevaluation involves “touch DNA” – the invisible genetic markers we leave everywhere we go, and on virtually everything we come into contact with.

A two-minute handshake, 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, in the January issue of the Journal of Forensic Sciences.

“It’s scary,” said Cynthia Cale, a graduate student and author of the paper. “Analysts need to be aware that this can happen, and they need to be able to go into court and effectively present this evidence. They need to school the jury and the judge that there are other explanations for this DNA to be there.”

The concept of “touch DNA” needs to be rethought, in both a legal and scientific context, according to Madison Earll, the other graduate student who authored the study.

“This research highlights the need to eliminate ‘touch DNA’ from our vocabulary,” said Earll, now a microbiologist at Pace Analytical. “It’s clear that this term is misleading and does not adequately explain all of the possible ways that DNA can end up on an object.”

Read more: Widow Sues City after Husband, Linked to Cold-Case Murder, Commits Suicide

“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,” Cale wrote in a piece for the journal Nature. “This could place people at crime scenes that they had never visited or link them to weapons they had never handled.”

Cale cited an example of a man in California in 2013 who was held for a homicide for four months after his DNA was pulled from underneath the fingernails of the victim. However, it was later proven that the suspect was hospitalized and several intoxicated at the time of the crime – but the paramedics who had responded to him medically responded to the murder shortly thereafter, she wrote.

“It’s a small world,” a deputy district attorney reportedly said upon the innocent man’s release.

Other suspects have claimed their DNA was transported to incriminating places through contamination. A criminalist in a San Diego lab maintained his innocence of the killing of a girl in 1984, saying he had only worked in the lab near where the samples were originally analyzed. The criminalist killed himself before charges were brought.

The scientists said they plan to continue experiments into 2016, systematically reducing the two-minute handshake down to smaller time frames, they said.

“I think this issue has been swept under the rug,” said Krista Latham, the director of the school’s Molecular Anthropology Lab, and who oversaw the study by Cale and others. “It’s going to change the way the medicolegal system looks at DNA evidence.”

View Source