Fingerprint Detection

Researchers at the University of Leicester, UK, working with Northamptonshire Police, have found a new technique for identifying fingerprints on metal. This method will enable forensic scientists to ‘visualise fingerprints’ even after the print itself has been removed. What is even more interesting is that this technology could ‘enhance — after firing — a fingerprint that has been deposited on a small calibre metal cartridge case before it is fired.’ As said the lead researcher, ‘For the first time we can get prints from people who handled a cartridge before it was fired.’ They add that ‘cases dating back decades could be reopened because the underlying print never disappears.’ But read more…

This research project has been led by Dr John Bond, the Manager of the Northamptonshire Police Scientific Support Unit, and an Honorary Fellow of the University of Leicester Forensic Research Centre. For a list of other research projects, here is a link to a news release from the Northamptonshire Police about the collaboration with the University of Leicester (May 19, 2008).

Here are some quotes from Bond about this new technique to discover fingerprints on metal surfaces. “Wiping it down, washing it in hot soapy water makes no difference — and the heat of the shot helps the process we use. The procedure works by applying an electric charge to a metal — say a gun or bullet — which has been coated in a fine conducting powder, similar to that used in photocopiers. Even if the fingerprint has been washed off, it leaves a slight corrosion on the metal and this attracts the powder when the charge is applied, so showing up a residual fingerprint. The technique works on everything from bullet casings to machine guns. Even if heat vaporises normal clues, police will be able to prove who handled a particular gun.”

But will this research be useful? “As a result of the research, cases dating back decades could be reopened because the underlying print never disappears, say the scientists. The technique also works in cases where prints may be left on other metals.” And Dr Bond added: “It’s certainly possible hundreds of cold cases could be reopened because with this method the only way to avoid a fingerprint being detected is through abrasive cleaning as that takes a layer off the metal.”

For more information about the fingerprint research projects under progress at the University of Leicester Forensic Research Centre, please visit this page to learn more about fingerprint enhancement on metal surfaces. “This research has demonstrated the ease with which it is possible for eccrine rich fingerprints to corrode a wide range of metal surfaces (both elements and alloys). The corrosion process has been shown to be dependent on the concentration of chemically aggressive chloride ions present in eccrine sweat. The water content of the fingerprint residue (over 99% of a fingerprint is made up of water) acts as an electrolyte to permit galvanic corrosion to take place over the surface of the conducting metal. This corrosion of the metal surface has been exploited by the development of a new technique to enhance fingerprints that requires the metal surface to be electrically charged to ~ 2,500kv followed by the application of a granular conducting powder. This technique (currently the subject of a patent application) has been used to demonstrate a solution to the extremely difficult problem of enhancing a fingerprint placed on a small calibre metal cartridge case prior to firing.”

This research work has been published online on May 9, 2008 in the Journal of Forensic Sciences, a Blackwell Publishing journal, under the name “Visualization of latent fingerprint corrosion of metallic surfaces.” Here is the abstract. “Chemical reactions between latent fingerprints and a variety of metal surfaces are investigated by heating the metal up to temperatures of 600°C after deposition of the fingerprint. Ionic salts present in the fingerprint residue corrode the metal surface to produce an image of the fingerprint that is both durable and resistant to cleaning of the metal. The degree of fingerprint enhancement appears independent of the elapsed time between deposition and heating but is very dependent on both the composition of the metal and the level of salt secretion by the fingerprint donor. Results are presented that show practical applications for the enhancement to fingerprints deposited in arson crime scenes, contaminated by spray painting, or deposited on brass cartridge cases prior to discharge. The corrosion of the metal surface is further exploited by the demonstration of a novel technique for fingerprint enhancement based on the electrostatic charging of the metal and then the preferential adherence of a metallic powder to the corroded part of the metal surface.”

Sources: University of Leicester news release, June 2, 2008; and various websites