If you don't know what it is, you should. I remember sitting next to C. Ken Williams at the ABA Prescription on Forensic Science the first time I'd heard of it, saying it was a huge deal. And a huge problem in forensic DNA analysis.
"The question sent to the lab seemed relatively simple. But the answer was incredibly complex.
A ski mask left behind after a bank robbery was the piece of evidence. The fabric showed a mixture of touch DNA including four people, but due to its complexity, it initially appeared as a mixture of only two people. The labs were given two of the four likely contributors, along with a fifth person.
But that fifth person was not in the mixture, and had never touched the ski mask.
It’s not a real case. It’s a hypothetical, a test; part of an inter-laboratory study involving more than 100 labs conducted by the National Institute of Standards and Technology.
Seventy percent of the labs got the wrong answer, by including that fifth, and innocent, person within the mixture.
The results showed that, as DNA sensitivity has grown by leaps and bounds, interpretation of those tiny clues has not kept pace. But those results were reached five years ago—and the study has not yet been published in a peer-reviewed journal. NIST says they have pushed out the results to other experts at major forensic conferences in the ensuing years—and now plan to submit a full paper to a major journal by the end of this month.
Critics say that justice has been deferred by the years-long delay, potentially landing untold numbers of people in prison based off faulty DNA mixture interpretation methods. Some experts said they were unaware of the potentially fortune-reversing findings—and others said the results were turned aside by judges because there was no official publication of the findings.
Just how many criminal cases were impacted by these mixture interpretation methods during the last five years—and even earlier than that—remains to be seen.
“This is about five years of people being convicted by bad interpretations,” said Greg Hampikian, a Boise State DNA expert. “This is a huge story. It’s the problem with DNA—the one everyone trusts.”