Criminal forensics: science without the science?

It's hard not to be impressed with the scientific developments of forensic investigation in recent years. What DNA, hair-and-fiber evidence, and even dirt and water samples can tell police is truly amazing. Making the public impression of forensic infallibility all the greater are, of course, the CSI shows, which inexplicably put forensic investigators in the role of ... well, doing everything we might have been forgiven for thinking that actual police do. TV is like that. (Contrast that with the "real" forensics shows on TruTV -- formerly CourtTV -- and the Discovery family of channels, where they pretty much stay in the lab or head to the crime scene, without actually staring down the bad guys with guns drawn.)

The past two years have cast a pall on the supposed infallibility of forensic evidence, however, and New Scientist's online technology editor Tom Simonite brings another chink in the armor to light: Gunshot residue (GSR) evidence, which is not even all that new in the investigator's portfolio. Turns out GSR is of limited value, as the case of Barry George in the UK has made clear. George was convicted of killing TV presenter Jill Dando based on one tiny speck of GSR and little else. As Simonite notes:

That evidence was later rejected on appeal, when the defence made the case that it may have been transferred there from firearms officers involved in the investigation. A retrial today decided there had never been sufficient evidence to convict George.

This comes too late to keep George from serving prison time -- 9 years' worth.

This isn't the first time New Scientist has turned up serious problems (as opposed to defense attorney stratagems) with forensic evidence. The old theory that GSR could determine whether someone had fired a gun has its own sharp critics in the forensics field, as NS's Robin Mejia reported:

Some specialists argue for a more cautious approach. "None of what we do can establish if anybody discharged a firearm," says Ronald Singer, former president of the American Academy of Forensic Sciences and chief criminalist at the Tarrant county medical examiner's office in Fort Worth, Texas.

Peter De Forest of John Jay College of Criminal Justice in New York goes further. "I don't think it's a very valuable technique to begin with. It's great chemistry. It's great microscopy. The question is, how did [the particle] get there?"

The point here is not that forensic evidence is too flawed to use; to the contrary, it's often part of a compelling prosecution. It's just that forensic evidence is no trump card. There is, in fact, no trump card in terms of evidence -- everything from confession to DNA has been successfully challenged, and eyewitness evidence is notoriously shaky. To say nothing of fingerprinting, as NS uncovered in James Randerson and Randy Coughlin's 2004 report:

Contrary to what is generally thought, there is little scientific basis for assuming that any two supposedly identical fingerprints unequivocally come from the same person. Indeed, according to a report published in December, the only major research explicitly commissioned to validate the technique is based on flawed assumptions and an incorrect use of statistics. The research has never been openly peer reviewed.

This month, the US government also published a set of funding guidelines that rules out further studies to validate both fingerprint evidence and other existing forensic techniques presented as evidence in court. In 2003, a proposal by the US National Academies to validate such techniques collapsed after the Department of Defense and Department of Justice demanded control over who should see the results of any investigation.

Forensic evidence is vital, but it's part of the big picture -- and juries need to bear this in mind, even as they remind themselves that TV is just that, and nothing more. Forensic studies are equal parts science and guesswork, far from the guarantors of justice such evidence is often portrayed as. And seeking justice, letting the chips fall where they may, is what our system alleges to be all about. We should be more skeptical, and demand more from the system.