Everyone knows that eye-witness testimony is highly dubious in court, and what you really want is some hard and fast forensic evidence, tested at the police lab, demonstrating with scientific accuracy who the guilty party is.
Or … maybe not.
Instead, to judge by the most comprehensive study on the reliability of forensic evidence to date, the error rate is more than 10% in five categories of analysis, including fiber, paint and body fluids. (Meaning: When the expert says specimen X matches source Y, there’s a 10% probability he’s wrong.) DNA and fingerprints are more reliable but still not foolproof. The 1995 study, in the Journal of Forensic Sciences, looked at proficiency tests labs take to see whether their work is sound.
More recent studies have also shown problems. Though a 2005 study in the Journal of Criminal Law & Criminology suggests a fingerprint false-positive rate a bit below 1%, a widely read 2006 experiment shows an alarming 4% false-positive rate.
The article recommends lab competition and privatization. I’m not sure that’s quite the right way to go — but I do recall from my environmental remediation days that we had a wide array of lab validation techniques: splitting samples for separate testing, sending in dummy samples of known quantities, using secondary labs for confirmation, etc.
Granted, crime scene evidence isn’t exactly like soil samples, and some evidence is so scant or unitary that it wouldn’t allow for easy splitting or reconfirmation. But there’s a lot you could do to test in a lot of cases, and to improve the quality of the results. Lives — innocent and guilty alike — can be at stake.