"How many cases of innocent people being wrongly convicted have to occur before people realize that there's a very broad spectrum of forensic science?" asks U.S. District Court Judge Jed Rakoff, a former member of the National Commission on Forensic Science.
For the past five decades, FBI examiners have used image comparison to tie defendants to crime scenes. Image comparison has been used in thousands of cases, yet studies have shown several of its underlying techniques to be scientifically unreliable.
That ought to mean that image comparison evidence does not get used in court. After all, in 1993's Daubert v. Merrell Dow Pharmaceuticals Inc., the U.S. Supreme Court ruled that courts should never admit expert testimony without first assessing the scientific validity of the underlying reasoning and methodology.
Yet when it comes to image comparison, the main supporting study is at least 22 years old. Over the last decade, both the FBI and other scientists have conducted other studies that have found the technique unreliable.
Nevertheless, image comparison examiners continue to testify that they can match images with great scientific certainty.
The nonpartisan, nonprofit newsroom ProPublica recently published a detailed analysis of the FBI's claims and the scientific reality of image comparison as a forensic technique. The analysis is too long to cover in a blog post, and we recommend reading the entire piece.
The FBI has a history of flawed and exaggerated forensic testimony
As ProPublica points out, the idea that the FBI would use unscientific methods to gather evidence and then exaggerate their degree of scientific certainty under oath is a familiar one. More than once, the agency has been found to have relied on methods with little or no scientific underpinning, including microscopic hair analysis, bite mark analysis, blood spatter analysis, and shoe and tire tread analysis.
In some cases, the FBI itself discovered the flaws in the techniques. In others, third-party reports revealed the problems. In 2009, the National Academy of Science issued a report concluding that "with the exception of nuclear DNA analysis ... no forensic method has been rigorously shown to have the capacity to consistently, and with a high degree of certainty, demonstrate a connection between evidence and a specific individual or source."
Yet FBI examiners have repeatedly testified that they could use these techniques to identify defendants "to the exclusion of all others." Last year, the Justice Department issued new testimony guidelines that prohibit examiners from making unequivocal statements like that.
One reason these flawed and exaggerated methods are brought into court is that prosecutors continue to submit the evidence -- and judges continue to accept it. That has to change, or more innocent people will end up behind bars.