Today, most of us see DNA evidence as terrifically persuasive: A 2005 Gallup poll found that 85 percent of Americans considered DNA to be either very or completely reliable. Studies by researchers at the University of Nevada, Yale, and Claremont McKenna College found that jurors rated DNA evidence 95 percent accurate and between 90 and 94 percent persuasive, depending on where the DNA was found. That faith could be shaken, but only when lawyers made a convincing case that a lab had a history of errors.
Otherwise, the mere introduction of DNA in a courtroom seemed to stymie any defense.
“A mystical aura of definitiveness often surrounds the value of DNA evidence,” the studies’ authors wrote.
In many cases, this aura is deserved. The method is unequivocal when it tests a large quantity of one person’s well-preserved genes, when it’s clear how that evidence arrived at a crime scene, and when the lab makes no errors in its work.
But those are not circumstances enjoyed by every criminal investigation.