Juries tend to find forensic evidence extremely convincing, which is why prosecutors in Florida and around the country rarely question the science supporting it. This reluctance to draw attention to the flaws of evidence that often secures convictions could explain why it took the Department of Justice almost five years to respond to a 2016 report from the President’s Council of Advisors on Science and Technology. In that report, PCAST researchers highlighted the lack of scientific data supporting forensic feature-comparison methods and called for some techniques to be discarded.
The methods mentioned in the report involve comparing evidence discovered at crime scenes with evidence collected from a suspect. The report cited comparing bite marks on a victim with a suspect’s dental records as an example of this method, and it concluded that the technique has little or no probative value. Groups advocating for justice system reform and criminal defense attorneys may have been unsurprised by this conclusion because these methods were developed by law enforcement and not the scientific community.
The scientific debate over the reliability of forensic evidence has drawn attention to cases involving innocent people who spent years in prison because experts either made mistakes or misled juries. According to research conducted by the National Registry of Exonerations, about one in four of the almost 3,000 people wrongly convicted since 1989 were sent to prison at least in part because of misleading or false forensic evidence. When the DOJ finally responded to the PCAST report on Jan. 13, the agency dismissed the findings and described them as “wrongheaded and incorrect.” Groups including the Union of Concerned Scientists have asked the DOJ to retract the statement.
Expert witnesses and jury instructions
Criminal defense attorneys may seek to limit the impact of questionable forensic evidence in three ways. They could file motions to suppress the evidence supported by scientific research like the PCAST report, or they could ask the judge to inform juries about the questions surrounding its reliability. When possibly unreliable evidence is allowed, defense attorneys could call expert witnesses of their own to ensure that juries hear both sides of the scientific argument.