Hanratty said he was in Rhyl at the time of the murders

Hanratty, 25, was hanged in 1962 for murder and rape but he always protested his innocence, claiming he was in north Wales at the time.

Solicitor Geoffrey Bindman said the family believed that the samples could have been contaminated and that proving Hanratty's guilt in this way was a "logical impossibility".

Hanratty, 25, was executed for killing government scientist Michael Gregsten, 36, and raping his 22-year-old lover Valerie Storie before shooting her and leaving her for dead in the notorious A6 murder case.

He always protested his innocence, saying he was at a guest house in Rhyl at the time of the killings.

At the time of his trial exhibits were handled freely because ... people did not know about DNA

Geoffrey Bindman Family solicitor

His body and that of his aunt, Annie Cunningham, were exhumed from Carpenders Park Cemetery in Bushey, Hertfordshire, last month so that police could gather evidence to support his conviction at an appeal hearing.

Now it has been confirmed that DNA extracted from Hanratty's teeth for examination by experts at the Forensic Science Service laboratory in Birmingham has been matched to samples from the crime scene.

Mr Bindman said the test results would prove very little.

"It is a logical impossibility for these tests to prove that Hanratty was guilty," he said. "The most that they can prove is that Hanratty's DNA was similar or the same to that which was found on clothing at the scene of the crime."

'Exhibits handled'

He said the question of how Hanratty's DNA got on to the samples remained open, with one possibility being that he was the murderer.

"Another possibility was that it got there because the clothing came into contact with his DNA from some other sources," he said.

"We know that at the time of the trial exhibits were handled freely because of course people did not know about DNA."

Hanratty's nephew, Michael Hanratty, said the family believed that the samples had been contaminated.

"We knew that it would come back like this," he said.

Mr Bindman said that the Criminal Cases Review Commission, which referred the case to the Court of Appeal, had been "well aware" that DNA samples were almost certainly from a member of the Hanratty family.

Samples found

Previous tests had already established a close match between the crime scene DNA evidence and samples taken from Hanratty's brother and mother.

Samples of their DNA were found to match traces found on Valerie Storie's underwear and a handkerchief wrapped around the murder weapon.

"This new evidence does not really take the matter much further than it was when the Criminal Cases Review Commission decided that the case should be referred to the Court of Appeal," said Mr Bindman.

The Court of Appeal hearing is expected later this year.