Page last updated at 23:08 GMT, Monday, 15 September 2008 00:08 UK

Fast-food could betray criminals

The technique can only be used to find fingerprints on metal surfaces

Criminals with an appetite for fast food could be tracked down more easily with a new fingerprinting technique that utilises the salt in their sweat.

Police can now detect corrosion left on metal by finger-tip sweat - the saltier the diet, the more the metal corrodes.

The technique works better than traditional fingerprinting which relies on residue that can be wiped away.

Northamptonshire Police's Dr John Bond, who developed the method, said it had so far been used in four active cases.

He said: "On the basis that processed foods tend to be high in salt as a preservative, the body needs to excrete excess salt which comes out as sweat through the pores in our fingers.

"So the sweaty fingerprint impression you leave when you touch a surface will be high in salt if you eat a lot of processed foods - the higher the salt, the better the corrosion of the metal."

High temperatures

Dr Bond, who is also a researcher at the University of Leicester, said the technique could only be used to find prints left on metal surfaces.

But he said the new method could find prints where traditional fingerprinting drew a blank because finger-tip residue had been wiped away or obliterated by high temperatures.

He also said the corrosive mark started by the salt could even be enhanced by high temperatures which exacerbate corrosion in metal.

We would describe the study of sweat as a process of intelligent fingerprinting
Dr John Bond
Northamptonshire Police

In all four cases where the method has so far been put to use, the prints have been on metal that has experienced high temperatures, such as shell casings expelled from guns after a bullet had been fired.

In one of the cases, Dr Bond said, an investigation into a 1999 double murder in the US state of Georgia had been re-opened because of evidence garnered by the method.

Dr Bond said the technique might also be useful in terrorism investigations to detect prints left on metal debris left behind after bomb blasts.

Other techniques

The research into sweat had also thrown up other possible forensic techniques, he added.

Just as the salt component in people's sweat varies greatly, Dr Bond suggests that other elements found in sweat may also vary in accordance with other factors such as ethnicity, gender, age or where you live.

He said this aspect of his research was at a highly conjectural stage, but that it might lead to ways of tracking down criminals through the traces of sweat they left behind.

He added: "We would describe the study of sweat as a process of intelligent fingerprinting - using the fingerprint to tell us more about the individual rather than a simple identification."

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