The fingerprint on a bullet casing was identified using an old shoebox and forensic tape
Forensic experts at Northamptonshire Police could help solve a double murder case in America.
Dr John Bond, the force's scientific support manager, has developed techniques to find prints on metal.
In 1999 two men were shot dead during a robbery at an auto pawn shop in Georgia but fingerprint analysis of the gun shells previously proved inconclusive.
A US detective travelled 4,000 miles to the UK to use the technology and found a fingerprint on a small shell case.
The new technique enables scientists to visualise fingerprints even after the print has been removed.
An electric charge is applied to metal objects which have been coated in a fine conducting powder.
A removed fingerprint would leave a slight corrosion on the metal which would be revealed by the powder.
Det Christopher King, who travelled to Northamptonshire from the US, said: "The tests we have done on these shell casings have given us a good result that we will be taking back.
"We can now at least eliminate some of the people that we are looking at and we may be able to at least make a tentative identification."
There has also been interest in the new forensic techniques from police forces across America hoping to solve thousands of unsolved cases.
The US military has also expressed an interest in the technique which could find prints on roadside bombs, Dr Bond said.
It could mean recovered fragments of bombs could be tested for prints left on them while they were being manufactured.
Northamptonshire Police announced in May that it had joined forces with experts at the University of Leicester Forensic Research Centre to develop the new technique.
Dr Bond said they had found the method worked well on certain metals including brass which is often used for bullet casing.
He said they now thought they could also use it on fragments of bombs to find bombers' prints.