A cold case review of the homicide, which took place almost a decade ago in Kingsland, Georgia, has been opened to try to catch two or possibly three suspects.

The US police read about a new fingerprint testing technique developed by Northamptonshire Police's forensics expert, Dr John Bond.

And this week Det Chris King, of Kingsland Police Department, flew to the UK with four bullets from the crime scene.

Det King said: "Both the victims were good, family men. Every year on the anniversary, their families call in to check up on how we are doing and it would be wonderful to have some news this year."

But he added: "We will be very lucky if we find anything and we are being realistic."

The murders took place on December 1, 1999, when the suspects entered a loan business for a routine robbery.

They ended up "executing" two men who were working in the shop, before making off with just a few hundred dollars.

Det King added: "This is not the only unsolved murder case we have in Kingsland at the moment, but it is the only one with any realistic hope of being cracked. We have some suspects in mind.

"Coming to the UK shows how important solving this case is to us. We have got to try everything."

Dr Bond will examine four bullets for fingerprints of the culprits. His new technique can pick up prints even after metal has been cleaned or put through extreme heat; for example, after it has been fired from a gun.

He said: "The bullets in this case are smaller than the ones we have previously worked on, so that will make it a bit harder for us.

"But any work that has been done on them over the past 10 years will make no odds to the tests we will be doing, so we're hopeful."

Several police forces in the UK and the US, as well as the FBI and the US Marines, have already expressed interest in the method, which was developed by Dr Bond in his basement in the village of Wappenham, in partnership with the University of Leicester.