On the case

A probe used in metals analysis holds the key to detecting fingerprints on fired bullets.

Fingerprints could be obtained from fired cartridge casings or detonated grenades using a device capable of detecting electrochemical changes to metal – even after intense heat.

As global terrorism spreads and UK gun crime increases, police and forensics teams are stepping up efforts to catch the perpetrators. But obtaining fingerprint samples from firearms cartridge cases or explosive devices after they have been fired or detonated is notoriously difficult, as the traces of fat, amino acids or proteins that the dusting powder detects have been burnt off or largely altered.

Researchers at the University of Wales, Swansea, are investigating the use of a scanning Kelvin microprobe to detect the electrochemical changes made to metal surfaces when they come into contact with fingers.

Inorganic salts found in sweat deposited at fingerprint ridges alter the electrical potential, or amount of energy per unit of charge, of the area of metal they touch.

These changes create a fingerprint that can be detected by the microprobe – which is used to map the electrical potential of metal surfaces – without the need for dusting powders or other preparatory chemicals, said Dr Neil McMurray, senior lecturer at the university’s Materials Research Centre.

The fingerprints remain on the casing even after undergoing the intense heat of firing or explosion, and can last for over a month. They can also be detected by the probe under a coat of paint, oil or grease.

‘The discovery came about serendipitously. We were using a scanning Kelvin probe to study localised corrosion. When we presented the metal samples, we kept getting our fingerprints on them,’ said McMurray.

The probe detects these fingerprints as being up to 0.5V lower than the charge of thesurrounding surface, creating a high contrast.

The researchers will work with fingerprint experts at the Forensic Science Service (FSS) and Qinetiq on the project, which officially starts next February, although the team hopes to start work before this. The organisations will provide the team with fingerprint samples and expertise in standard forensic techniques.

As part of the project, which recently received around £200,000 in funding from the EPSRC, the researchers plan to upgrade their ‘home-made’ probe to make it more suitable for scanning cylindrical metal samples, such as cartridge casings.