ForensicsDNA identification may not be as reliable as previously thought

Published 4 November 2015

Increasingly important to criminal investigations, DNA analysis once required substantial samples of blood or other bodily fluids, but advances in the field now make it possible to produce a complete genetic profile of a suspect from just a few cells left behind — so-called “touch DNA.” A new study shows that secondary transfer of human DNA through intermediary contact is far more common than previously thought, a finding that could have serious repercussions for medical science and the criminal justice system.

Methodology of DNA comparison identification // Source: berkeley.edu

If your DNA is found on a weapon or at a crime scene, does that make you guilty? A judge or jury might think so, but a new study from the University of Indianapolis shows that secondary transfer of human DNA through intermediary contact is far more common than previously thought, a finding that could have serious repercussions for medical science and the criminal justice system.

Increasingly important to criminal investigations, DNA analysis once required substantial samples of blood or other bodily fluids, but advances in the field now make it possible to produce a complete genetic profile of a suspect from just a few cells left behind — so-called “touch DNA.”

UIndy reports that the emerging concern, long considered a theoretical risk but only now systematically confirmed by the UIndy study, is that the presence of those cells does not prove that the person actually visited the scene or directly touched the object in question. The DNA easily could have been transferred by other means.

I think this issue has been swept under the rug,” said Associate Professor Krista Latham, who directs UIndy’s Molecular Anthropology Laboratory and oversaw the study designed as a course project by Human Biology graduate students Cynthia Cale and Madison Earll. “There have been some holes in this kind of research, and I think that allowed people to disregard it, but this is a very well-designed project. It’s going to change the way the medicolegal system looks at DNA evidence.”

The researchers detail their findings in the January issue of the Journal of Forensic Sciences. Cale also discusses the study in an op-ed for this week’s issue of the journal Nature.

Cale is lead forensic DNA analyst at Strand Diagnostics, an Indianapolis-based laboratory that provides services to public agencies and has a collaborative partnership with UIndy’s Department of Biology. Like Latham, she has served often as an expert witness for court proceedings involving DNA analysis. The new study was inspired by a concern that arose at the Strand laboratory, after routine contamination checks began turning up DNA profiles of people who had never been there — the employees’ children.