Mark Joseph Stern in Slate:
Far from an infallible science, forensics is a decades-long experiment in which undertrained lab workers jettison the scientific method in favor of speedy results that fit prosecutors’ hunches. No one knows exactly how many people have been wrongly imprisoned—or executed—due to flawed forensics. But the number, most experts agree, is horrifyingly high. The most respected scientific organization in the country has revealed how deeply, fundamentally unscientific forensics is. A complete overhaul of our evidence analysis is desperately needed. Without it, the number of falsely convicted will only keep growing.
Behind the myriad technical defects of modern forensics lie two extremely basic scientific problems. The first is a pretty clear case of cognitive bias: A startling number of forensics analysts are told by prosecutors what they think the result of any given test will be. This isn’t mere prosecutorial mischief; analysts often ask for as much information about the case as possible—including the identity of the suspect—claiming it helps them know what to look for. Even the most upright analyst is liable to be subconsciously swayed when she already has a conclusion in mind. Yet few forensics labs follow the typical blind experiment model to eliminate bias.