What's Wrong With CSI

Forensic evidence doesn't always tell the truth.

Forensic evidence is foolproof, right? It's how those clever cops on CSI always catch the killer. DNA evidence springs innocent men from prison. Fingerprints nab the bad guys.

If only forensics were that reliable. 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 core problem with the forensic system is monopoly. Once evidence goes to one lab, it is rarely examined by any other. That needs to change. Each jurisdiction should include several competing labs. Occasionally the same DNA evidence, for instance, could be sent to three different labs for analysis.

This procedure may seem like a waste. But such checks would save taxpayer money. Extra tests are inexpensive compared to the cost of error, including the cost of incarcerating the wrongfully convicted. A forthcoming study I wrote for the Independent Institute (a government-reform think tank) shows that independent triplicate fingerprint examinations in felony cases would not only eliminate most false convictions that result from fingerprint errors but also would reduce the cost of criminal justice if the false-positive error rate is more than 0.115%, or about one in a thousand.

Other reforms should include making labs independent of law enforcement and a requirement for blind testing. When crime labs are part of the police department, some forensic experts make mistakes out of an unconscious desire to help their "clients," the police and prosecution. Independence and blind testing prevent that. Creating the right to a forensic expert for the defense would help restore the imbalance in scientific firepower that too often exists between prosecution and defense. Private labs are subject to civil liability claims and administrative fines, giving them financial incentives to get it right.

These all sound like great ideas. If the goal of criminal investigation is to convict the guilty and protect the innocent, there seems to be little reason not to put these ideas into action. If the studies mentioned above are correct, these changes would lower costs and increase accuracy. They also represent a policy change that would satisfy both utilitarian and retributivist notions of justice.

(HT Don Boudreaux)