Detectives could soon be looking for traces of breath from criminals in the same way they look for fingerprints, according to reports.

In the centenary year of the first prosecution using fingerprint evidence, police are being given advice on how to preserve crime scenes for a new DNA technique, the Independent reported.

Droplets of moisture coming from the mouth during speech can be left on masks, telephones or other surfaces.

Bigger traces would be left if the criminal had coughed.

The Central Police Training and Developmental Authority (Centrex) is teaching the technique to officers to avoid potentially valuable evidence being destroyed, the paper said.

Skin evidence

Officers arriving at a crime scene could be contaminating evidence with their own breath and might eventually wear protective clothing as a matter of course.

Andy Humphreys, head of operations at Centrex, said: "We are moving to a position where it's difficult to see how somebody will be able to avoid leaving a trace when they enter a room if that trace comes from the fact they are going to have to breathe."

The paper said research is continuing to see how long breath and skin DNA evidence would last at a crime scene.

Researchers also want to find out if it is possible to transfer someone else's DNA to the crime scene, such as that coming from a handshake.

A study by the City of London police and the South Bank University led to the arrest of 21 computer thieves using DNA swab evidence.

The techniques involved are a significant improvement on what is currently available.