The uniqueness of DNA evidence has been brought into question once again by a lab tech in Arizona: http://www.latimes.com/news/local/la-me-dna20-2008jul20,0,1506170,full.story
The tech discovered two criminals on the database with remarkably similar DNA, close enough in fact to satisfy a court of a match in most cases. One was white, the other black. She went on to discover nearly 1000 more matching pairs.
Police in the UK are still using discredited Low Copy Number DNA evidence, despite it being the cause of the collapse of the Omagh bomb trial. In that case there were also two people that the DNA pointed too, one of whom was a schoolboy living in England.
Claims that the chances of a false DNA match are billions to one are now clearly discredited, yet the police carry on using DNA in this way and relying on it in court. Unsurprisingly, lawyers are now starting to demand extensive database searches and finding their own expert witnesses to counter this. Like fingerprint evidence, it appears that soon DNA evidence will be reduced in importance and police will have to rely on other, more traditional forms of proof when bringing a case.
It will be interesting to see the outcome of the Barry George re-trial too – yet again, forensic evidence (a single particle of gunpowder) has been overstated at trial.