Silent witness reveals clues to crime
21 Mar 2011 by Evoluted New Media
Did they jump or were they pushed? Questions like this can be difficult for the police to answer, but a new technique to visualise fingerprints on fabrics may help convict criminals.
Did they jump or were they pushed? Questions like this can be difficult for the police to answer, but a new technique to visualise fingerprints on fabrics may help convict criminals.
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A 21-day sample on nylon demonstrating palmar flexion creases Credit: University of Abertay Dundee/Scottish Police Services Authority. |
Vacuum metal deposition (VMD) is a highly sensitive technique already used to detect fingerprint marks on smooth surfaces like plastics, glass and carrier bags, but it is now being used in the examination of clothing thanks to research from Scotland.
Forensic experts at the University of Abertay Dundee and the Scottish Police Services Authority (SPSA) hope VMD could be used alongside other evidence to present a more robust case to the court.
“An impression could help the police piece together a timeline of events and could be used to provide evidence in cases where someone was pushed, or grabbed, in a particular part of their clothing,” said Paul Deacon, fingerprint unit manager at the SPSA. “An impression of a palm print on the back of someone’s shirt might indicate they were pushed off a balcony, rather than jumping.”
The technique uses fine layers of metals to display fingerprints left on fabrics said Joanna Fraser, a forensic sciences researcher at Abertay.
“We take these fabrics, place them in a vacuum chamber, then heat up gold to evaporate it and spread a fine film over the fabric,” Fraser said. “We then heat up zinc, which attaches to the gold where there are no fingerprint residues. This helps reveal the fingerprint.”
She likened the result to a photographic negative where colours show up as opposites: “Where contact has been made we see the original fabric, where there was no contact we’re left with the grey colour of the metal film.”
Fraser said the challenge is now to develop the technique further and confirm its effectiveness. The technique has proved successful for revealing the shape of a handprint on a number of types of fabric – those with high thread count give the best print, but they have been recovered from silk, nylon and polyester. Despite this achievement, only 20% of the public are classed as ‘good donors’ for leaving fingerprints so the success rate of recovering a full fingerprint from an item of clothing is still low.
