Fingerprints are Forever: Forensic Watershed

To visualise the patterns, Bond's technique involves passing 2500 volts through the metal and sprinkling a fine conducting powder on it. While the electric field is applied, the powder sticks to the corroded areas.

"If the corrosion's there, it will stay there unless you abrasively clean the metal. The only way to get rid of it is to actually take the surface layer of the metal off," he said. "Some metals corrode very well and some not at all. One metal that works very well is brass and gun cartridge cases happen to be made of brass."

He has published details of the technique in the latest issue of the Journal of Forensic Sciences. In his paper he demonstrates that it is possible to recover fingerprints from a bullet casing ejected when a pistol is fired. "As you are pushing the magazine in you are actually putting a thumb print on the bullet," said Bond. "That's the person you want. That's the guy who loaded the gun."

The Metropolitan Police has asked Bond to look into evidence kept from a 10 year old murder case. He is also using the technique on evidence from a recent murder that is being investigated by Lincolnshire police.