LONDON, England (CNN) — A groundbreaking technique that enables scientists to detect fingerprints on spent bullets and shell casings, even when the print was wiped clean, has been developed in Britain and may help police & forensic scientists break cold cases.  The technique works by detecting the corrosion of metal caused by sweat.  The slightest bit of sweat is instantly imprinted on metal and leaves a corrosion in the shape of a fingerprint, giving police the ability to match those prints with fingerprints of possible suspects; something they were unable to do unless they uncovered an actual dusted fingerprint.