Judge Alex Kozinski  wrote a very interesting commentary on forensic science in criminal cases for The Wall Street Journal:

“The White House will release a report Tuesday that will fundamentally change the way many criminal trials are conducted. The new study from the President’s Council of Advisors on Science and Technology (PCAST) examines the scientific validity of forensic-evidence techniques—DNA, fingerprint, bitemark, firearm, footwear and hair analysis. It concludes that virtually all of these methods are flawed, some irredeemably so.

Americans have long had an abiding faith in science, including forensic science. Popular TV shows like “CSI” and “Forensic Files” stoke this confidence. Yet the PCAST report will likely upend many people’s beliefs, as it should. Why trust a justice system that imprisons and even executes people based on junk science?

Only the most basic form of DNA analysis is scientifically reliable, the study indicates. Some forensic methods have significant error rates and others are rank guesswork. “The prospects of developing bitemark analysis into a scientifically valid method” are low, according to the report. In plain terms: Bitemark analysis is about as reliable as astrology. Yet many unfortunates languish in prison based on such bad science.

Even methods valid in principle can be unreliable in practice. Forensic scientists, who are often members of the prosecution team, sometimes see their job as helping to get a conviction. This can lead them to fabricate evidence or commit perjury. Many forensic examiners are poorly trained and supervised. They sometimes overstate the strength of their conclusions by claiming that the risk of error is “vanishingly small,” “essentially zero,” or “microscopic.” The report calls such claims “scientifically indefensible,” but jurors generally take them as gospel when presented by government witnesses who are certified as scientific experts.

The full piece can be found here.