Friday, April 11, 2008
I've written twice before (here and here) about how the United Kingdom suspended its use of "low copy number" DNA. As I noted, low copy number DNA allows the genetic profiles of suspects, victims or witnesses to be "uncovered" even when there is only a tiny amount of biological material present, sometimes as small as a millionth of the size of a grain of salt. The technique amplifies these tiny DNA fragments when it is believed that a suspect may have transferred DNA through touch, like the residue believed to have come from cells such as skin or sweat left in a fingerprint.
In the wake of the disastrous Sean Hoey case, however, the Crown Prosecution Service ordered a re-examination of current cases relying on low copy number DNA evidence, and the Association of Chief Police Officers suspended its use of it (although its use was subsequently reinstated). Well, that re-examination led to a report by scientists at the University of Strathclyde. The report found the technique to be scientifically sound and Professor Brian Caddy, who carried out the review, said it should not cause wrongful convictions. If the review had found problems with the science it could have triggered the re-examination of scores of criminal cases.
The review's authors did call for improvements in the collection of DNA from crime scenes and in its analysis to avoid the evidence becoming unusable. Specifically, Caddy made 21 recommendations to standardize procedures, including (1) ensuring that police evidence-gathering kits are "DNA-clean" to avoid contamination with someone else's genetic profile, (2) a national agreement on how to interpret the results from low-template DNA, and (3) clear guidance on how courts should interpret the evidence. The report's authors also voiced concern at the quality of forensic science conducted by police laboratories, which often analyze low-template DNA first.
As I noted before, low copy number DNA has been consistently doubted in the scientific community, and it has thus only been used in the U.K., the Netherlands, and New Zealand, which makes me wonder, as with the New Jersey report on the Alcotest 7110, whether this was a "politically motivated" report based upon the consequences that would have occurred had low copy DNA been found unreliable.