Fingerprints could soon help police narrow down their list of suspects by giving clues about the lifestyle of whoever left the prints at the scene of a crime.

The technique can spot prints invisible to naked eye

Researchers in the UK are uncovering the ways fingerprints are changed by age, smoking, drug use and even some personal grooming products.

The work also promises to help obtain good quality copies of prints that have gone unnoticed for days or weeks.

Related work aims to find prints on guns and bomb fragments that are often among the most difficult to recover.

Led by Dr Sue Jickells from Kings College, London, the work on getting more from fingerprints started by looking at the chemical components of prints and how they change over time.

Dr Jickells said much of the material left behind when people touch anything are fat molecules, or lipids.

"There are a lot of lipids in fingerprints," said Dr Jickells, "and there are a lot of possibilities for that."

Old evidence

One such lipid, called squalene which is a precursor to cholesterol, is heavily present in fingerprints.

Squalene breaks down over a period of days, as do the saturated and unsaturated fatty acids left behind by human touch. This makes it harder for traditional techniques to reveal prints.

Analysis shows up the details of the prints on the bullet

The research has also shown how fingerprints can be used to give clues about the person that left a print.

Dr Jickells said that adults, children and the elderly lay down different sorts of organic compounds in the prints.

Furthermore, drug users typically excrete the metabolised products of the chemical they use. For instance, smokers are known to secrete cotinine, a chemical produced when the human body breaks down nicotine.

Work is now going on with methadone maintenance clinics and cocaine addiction centres to see how drug use changes the prints users leave behind.

Revealing patterns

The complementary work by Professor Neil McMurray and colleagues at the University of Wales, Swansea, also aims to get more out of fingerprints left when the most serious of crimes are committed.

Professor McMurray's work shows how it is possible to recover fingerprints from the metal surfaces of bullets and shrapnel.

Prints left on guns and bomb casings tend to be patterns left by human sweat and, as such, are not easy to reveal using established techniques that employ powders and other chemicals.

Instead, Professor McMurray measures the tiny electrochemical reactions that result when fingers touch metal.

A device called a Scanning Kelvin Probe is used to measure the tiny changes in electrical potential caused by these reactions.

Print patterns have been found even on metal that has been subjected to temperatures of 600C.

The technique has been shown to work with iron, steel, aluminium, zinc and brass and can even cope with the curves found on bullets.

Professor McMurray said the end result of the research would be a portable device that could analyse prints at crime scenes.

The research on fingerprints was presented at an event in London organised by the Engineering and Physical Sciences Research Council to highlight how science can aid forensic work.