Fingerprints not clear enough? Try bacteria to nail your criminal

Police may soon be able to add another forensic tool to their armoury following a study showing that it is possible to identify a person from the bacteria they leave behind after touching an inanimate object such as a computer keyboard or telephone.

Fingerprints can provide an exact match between an object and someone who touches it, but the new technique exploits the fact that the microbial community living on someone's hands is sufficiently unique to a person for it to be used as another form of forensic identification.

Scientists said that with further development it might soon be possible for the police to take a swab from a piece of equipment and determine who was using it days, or even weeks, earlier, even where investigators are unable to recover any fingerprints.

A preliminary trial has shown that the new technique is between 70 and 90 per cent accurate in identifying someone who used a computer mouse.

"Each one of us leaves a unique trail of bugs behind as we travel through our daily lives. While this project is still in its preliminary stages, we think the technique could eventually become a valuable new item in the toolbox of forensic scientists," said Professor Noah Fierer of the University of Colorado at Boulder, who led the study published in the journal Proceedings of the National Academy of Sciences.

Research carried out in 2008 established that the combination of bacteria carried around on someone's hands - typically about 150 species - is pretty unique to them and is not affected by handwashing.

It identified more than 4700 bacterial species in total across the 102 hands examined, but only five of these species were shared by all 51 participants and only 13 per cent of the bacterial species found on a single hand were shared by any two people.

In the latest study, the scientists swabbed individual keys on the keyboards of three personal computers and were able to match them in terms of their mix of species to the bacteria living on the fingertips of each computer's owner.

In another test, the scientists were able to match nine computer mice that had not been touched for 12 hours to their owners, compared with a sample of 270 hands which had never touched the mice and whose palms had been swabbed for their bacterial flora.

Further tests showed that the bacterial community found on a computer mouse remained essentially unchanged after two weeks at room temperature.

- INDEPENDENT