Forensic science’s flaws are catching up with it
Jul 18th 2015 | From the print edition
Another forensic mess you’ve gotten me into
THE more that is known about a science, the more uses tend to be found for it. But in the case of forensics—the discipline through which villains are identified by stray fingerprints, stands of hair or other giveaways—it seems that the more is discovered about the field, the more courts are losing faith in it.
Advances in forensic science have led to spectacular breakthroughs in justice. In 2009 Sean Hodgson, who had spent 27 years in jail for the 1979 murder of a Southampton barmaid, had his conviction quashed after DNA tests proved that blood found at the crime scene could not have been his. But in other cases faulty forensic evidence has led police and prosecutors astray. In 2012 a man spent five months in jail awaiting trial for a rape committed in a city he had never visited, after a police lab confused his DNA with samples taken from the victim. In 2014, after spending 12 years in jail, Dwaine George had his murder conviction overturned after a retrial established that the tiny quantity of gunshot residue found on a coat in his house could have been picked up anywhere.
In America, concerns about forensic evidence are well established. Dodgy forensics contribute to nearly half of all wrongful convictions there, according to the Innocence Project, a New York-based charity dedicated to overturning miscarriages of justice. In 2009 America’s National Academy of Sciences argued that fingerprint, bite-mark and bloo-spatter analysis were being used unreliably. Earlier this year a report by a defence-lawyers’ association found hair analysis to be untrustworthy in 95% of cases.
As a result of such doubts, the use of some forms of forensic evidence has been suspended. In January a New York judge threw out evidence obtained from mixed DNA analysis, where two profiles are extracted from one sample. The FBI has abandoned the use of gunshot residue. Scepticism has grown in other countries, too: the Netherlands has given up the use of handwriting analysis, for instance.
Britain, on the other hand, remains keen on the Sherlock Holmes stuff. Mixed-DNA, gunshot residue and handwriting analysis are all still used in British trials, to the concern of some jurists. The profession has other problems, highlighted in a recent series of papers published by the Royal Society, a fellowship of eminent scientists. A restructuring of the national forensics service in 2011, in which the scientific analysis of crime-scene evidence moved from the public to the private sector, left it fragmented. According to two official reports that followed, this led to dangerous levels of disorganisation.
Problems are not limited to the lab. Scientists and lawyers come from different cultures with different languages, and can find it hard to explain things to each other in court. This makes it easier for barristers wilfully to misrepresent the evidence, according to Paul Roberts of Nottingham University’s school of law. Meanwhile jurors, educated by crime dramas, tend to overestimate what forensics can do—a tendency dubbed the “CSI effect” by lawyers.
The forensics profession has been slow to address its problems. And the erosion of forensic science’s credibility has happened so gradually that policymakers have not fully realised the scale of the problem, thinks Mr Roberts. This is worrying: cutting-edge science tends to be experimental, but justice should try not to be.
本文原文转自《经济学人》 翻译：石海霞 校对：吴倩