In with a bullet

1 August 2008

A new bullet-tagging technology being developed in the UK could give forensic teams a robust new tool in the fight against gun crime.

The breakthrough has been achieved by a multidisciplinary team from Brighton, Brunel, Cranfield, Surrey and York universities, with funding from the Engineering and Physical Sciences Research Council (EPSRC). Project partners include the Forensic Science Service, BAE Systems and coatings manufacturer Andura.

The tags, which measure 30 microns in diameter, are applied to gun cartridges by being embedded in cartridge coatings made from polylactic acid, sucrose ester and tetrahydrofuran. They then attach themselves to the hands or gloves of anyone handling the cartridge and are said to be very difficult to wash off.

A portion of the tag remains on the cartridge even after it has been fired, which could make it possible to establish a definitive forensic link between a cartridge fired during a crime and whoever handled it.

The current success rates for DNA profiling using evidence from gun cartridges are only around 10 per cent. To date it has been extremely hard to establish such a link because of the difficulty in retrieving fingerprints or significant amounts of DNA from cartridge surfaces.

‘The tags primarily consist of naturally occurring pollen, a substance that evolution has provided with extraordinary adhesive properties,' said Prof Paul Sermon from Surrey University, who led the research.

He added: ‘It has been given a unique chemical signature by coating it with titanium oxide, zirconia, silica or a mixture of other oxides.

'The precise composition of this coating can be varied subtly from one batch of cartridges to another, enabling a firm connection to be made between a particular fired cartridge and its user.’

The team has also developed a method of trapping forensically useful amounts of DNA on gun cartridges. It involves increasing the abrasive character of the cartridge case with micro-patterned pyramid textures, or adding an abrasive grit, held in place by a thin layer of resin, to the cartridge base.

This rough surface is able to retain dead skin cells from a thumb as it loads a cartridge into a firearm.

The technology has been designed to avoid damage to the DNA captured that is caused by temperatures generated as the gun is fired, when heat is rapidly transferred from the burning propellant into the cartridge case and when copper is extracted from the cartridge case by lactic acid in sweat.

The tag and DNA-capture technologies could potentially be available for use within as little as 12 months. There may also be scope to apply them in other fields, such as knife crime, in future.

‘We’re currently focusing on understanding the precise requirements of the police and cartridge manufacturers,’ said Prof Sermon. ‘But our work clearly could make a valuable contribution not only to solving gun crime but also to deterring criminals from resorting to the use of firearms in the first place.’