Detectives are using DNA material stored for six decades to try to trace the relatives of a man who raped and murdered a schoolgirl in 1946.

The investigation into the death of Muriel Drinkwater, 12, a Swansea grammar school pupil, is believed to be the world’s oldest cold case review.

Colin Dark, of the Forensic Science Service (FSS), said that if Muriel’s killer was still alive he was likely to be in his eighties.

The scientist, a cold case specialist, said that should a suspect be identified who had died, there would be a strong case for exhuming his body and carrying out DNA tests that could close the case.

Muriel was murdered in June 1946 as she walked home through woods from Penllergaer Grammar School.

She was known locally as the “little nightingale” because she always sang as she made her way to and from school.

On the day she died her mother saw her from a distance but lost sight of her as she took a path through Penllergaer Woods. When Muriel did not reemerge from the woods the alarm was raised and local people began searching for her.

Her body was found a little way off the path. The schoolgirl had been raped, battered about the head and shot twice at point-blank range, once through the heart. The murder weapon – an American Colt 45 automatic service pistol – was dropped at the scene.

Scotland Yard detectives were drafted in from London to help with the investigation but Muriel’s killer was never traced. The case lay dormant until South Wales Police’s major case review team decided to reopen it in 2003.

The gun was recovered from police archives and sent for DNA tests. But it had been handled by too many people and the results were inconclusive.

Officers then began searching for other evidence exhibits from the case, a task made more difficult because the local police station – where the investigation was based – had closed down.

Detective Chief Inspector Paul Bethell, a senior reviewer in the cold case unit, finally found the murdered girl’s blue school raincoat at the back of a cupboard.

Police identification tags had been lost but Muriel’s name was on a label sewn into the collar by her mother.

Dr Dark said: “We found staining on the inside of the coat flap, marked with yellow crayon just as it would be today, and set about recovering DNA and building a profile. It’s our oldest cold case and I think probably the oldest in the world.” Using the low copy number (LCN) technique, which allows DNA profiles to be obtained from microscopic or ageing samples, the scientists developed a profile.

There was no match on the national DNA database, however, and the scientists have now begun to search for relatives of the killer.

Dr Dark said: “We have produced a partial profile which allows us to conduct a familial search – we may find the suspect’s son or grandson.

“There were 40 or 50 names which featured in the original inquiry and the police will be seeing if they can connect any of those with any matches thrown up by the familial profile.”

Mr Bethell said the case raised the possibility of investigators reaching farther back in history to solve cases.

He said: “Closure is very important in cases like these, not just for families but also for the community. I’ve met people in Penllergaer who talk about this murder as if it happened last weekend.”

The FSS has conducted DNA tests in more than 500 cold case inquiries since 2000, when the use of LCN DNA profiling was stepped up. The reviews have resulted in about 120 convictions.

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