Correcting forensic DNA errors

Abstract

DNA mixture interpretation can produce opposing conclusions by qualified forensic analysts, even within the same laboratory. The long-delayed publication of the National Institutes of Standards and Technology (NIST) study of 109 North American crime laboratories in this journal demonstrates this most clearly. This latest study supports earlier work that shows common methods such as the Combined Probability of Inclusion (CPI) have wrongly included innocent people as contributors to DNA mixtures. The 2016 President's Council of Advisors on Science and Technology report concluded, "In summary, the interpretation of complex DNA mixtures with the CPI statistic has been an inadequately specified-and thus inappropriately subjective-method. As such, the method is clearly not foundationally valid" [7]. The adoption of probabilistic genotyping by many laboratories will certainly prevent some of these errors from occurring in the future, but the same laboratories that produced past errors can also now review old cases with their new software-without additional bench work. It is critical that laboratories adopt procedures and policies to do this.

Keywords: CPI; Criminal casework; DNA mixtures; Forensic errors; Legal and ethical issues; Mix13; NIST; Probabilistic genotyping; Quality control; TrueAllele.