A groundbreaking fingerprint technique has helped police move a step closer to solving a murder case on America's Most Wanted list, police said today.

The new technique, which finds fingerprints on bullets, has detected prints on bullet casings used in an unsolved doorstep shooting in a Texas suburb.

Dr John Bond, scientific support manager at Northamptonshire Police and honorary research fellow at the University of Leicester Forensic Research Centre, created the technique and was asked to help US police with the case.

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His new method of fingerprint 'visualising' detects where sweat has corroded metal on bullets, even where a print has been wiped off.

Today, Northamptonshire Police said he had found prints on bullet casings brought to the UK by Detective Tony Roten from North Richland Hills Police, Texas.

In the case, currently on America's Most Wanted website, 68-year-old Marianne Wilkinson was shot as she answered the door on the evening of 9 December last year.

Police are investigating whether it was a case of mistaken identity and if another woman in a nearby house was the intended target.

Det Roten said: "We are very pleased with Dr Bond's work.

"There appears to be good fingerprints on one of the casings."

The state-of-the-art technique, named by Time Magazine as one of the top 50 inventions of 2008, has already helped another American investigation.

Detective Chris King, from Kingsland Police Department, Georgia, recently visited the force to see if Dr Bond could help with a 10-year old unsolved double homicide case.

The initial findings which identified a partial print have helped US officers eliminate suspects in the case.

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Today Dr Bond said he had received calls from police forces from the UK and across the Atlantic asking for help with unsolved cases.

He said: "I have now examined in excess of 100 shell casings in the past couple of months.

"This current case for Detective Roten would appear to be the best print we have so far been able to enhance.

"We are very pleased that we have been able to help Detective Roten with this inquiry."