Crime labs across the nation were told that the FBI discovered errors in data related to thousands of cases used in calculations employed by forensic scientists to determine if DNA found at a crime scene is a match to a suspect.
The FBI believes the errors reach as far back as 1999, according to the Washington Post, but it is unlikely that cases will be affected. The research has been submitted to the Journal of Forensic Sciences for publication in the July issue.
"The public puts so much faith in DNA testing that it makes it especially important to make those the best estimates possible," said Wright State University statistics professor Daniel R. Krane. "There is no excuse for a systematic error to many thousands of calculations in such a context."
Krane said he flagged errors a decade ago, but his findings were ignored by the bureau, according to the Washington Post.
DNA matches are considered the "gold standard" of forensics. DNA profiles are typically built using 13 or more specific locations on chromosomes, called loci, for specific markers. A jury decision might not be affected if probabilities are dropped from 1 in 10 billion to 1 in a billion, but what if the probability dropped to 1 in 180? Krane recently testified in a case where that was the likelihood of a match, according to the Pittsburg Post-Gazette. The FBI is preparing to transition to a system that uses 20 or more loci.
The FBI said it found errors in 33 of 1,100 profiles used, or 3 percent. "We are of the view that these discrepancies are unlikely to materially affect any assessment of evidential value," the FBI stated in its May 11 bulletin to crime labs, according to the Washington Post. "However, given that statistics based on these data have been included in thousands of lab reports and in testimonies, we believe the discrepancies require acknowledgment."