An invisible dusting of dandruff or a sweaty palm could be enough to identify criminals, using a revolutionary DNA technique developed by an Australian researcher.
Dr Ian Findlay, of the Australian genome research facility at the University of Queensland, has managed to take DNA fingerprints from single cells with an accuracy of 10-billion to one. The technology, which is to be outlined at a science conference in Sydney today, could allow investigators to pick up DNA identities from pieces of plastic and even build up a complete history of the people who have handled a paper document.
”You’d have to wear a space suit to stop yourself from leaving traces. You can identify cells on the paper, so you can work out where it’s come from and who’s touched it,” he said.
The technique could also be used to trace the thrower of a punch from cells left behind on the skin of their victim. Even the wearing of latex gloves would not prevent contamination: small cells can pass through the gloves, and constant blizzard of genetic material given off by the human body would leave further evidence behind.
Typical DNA fingerprinting requires from 200 to 500 cells to produce enough material for a fingerprint, but the new techniques allow a print to be taken from a single cell. Dr Findlay says the technology eliminates the problems of contamination, because while normal profiles are taken from an aggregate of cells — some of which may come from different people — the new system relies on the evidence contained in one cell alone.
However, he admits that the system is unlikely to be used immediately. ”We have certainly shown that you can do it, but it’s getting it accepted in court that counts,” he says. Two sub judice cases before the Australian courts use the technology. One involves the extraction of DNA from decades-old fabric, while the other uses cells picked up from the surface of paper.
But Michael Strutt, an expert in forensic science formerly of the Australian rights group Justice Action, says that the sophistication of the technique could be its Achilles’ heel.
”If you have this sort of sensitivity you will pick up DNA all over everything. The more sensitive testing is, the less useful the results are as evidence, because you’ll be collecting more material and sowing more doubt in the minds of the jury.”
Police will normally pick up around 12 usable DNA samples in processing an average crime scene, and the amount would increase dramatically if only one cell was needed to produce a profile.
Such DNA evidence would also be unable to prove the nature of the link between the sample and suspect — simply being in the same room as a piece of evidence could be enough to leave a genetic mark on it.
However, Strutt did admit that the system could be a breakthrough in rape cases, where forensic scientists often have trouble telling which part of the DNA profile came from the perpetrator and which from the victim.
It could also be used to provide a definitive answer to cases like that of Jeremy Bamber, who was given a life sentence in 1986 for murdering his parents, sister and twin nephews in Essex.
Blood found on the silencer of the murder weapon was identified as belonging to Bamber’s sister, invalidating a defence argument that she had carried out the killings before turning the gun on herself. Earlier this month Bamber appealed his conviction, on the grounds that the DNA had been mixed from the blood of his parents and misidentified as the fingerprint of his sister.