James Hanratty claimed he was in Rhyl

He was convicted of murdering scientist Michael Gregsten on the A6 in Bedfordshire by shooting him twice in the head - but claimed he was 250 miles away in Rhyl, in north Wales.

Lord Woolf, the Lord Chief Justice, Lord Justice Mantell and Mr Justice Leveson have been urged to find Hanratty's 1962 conviction "unsafe".

Hanratty's relatives say his trial was "distorted", and that evidence was suppressed.

At the Appeal Court on Monday, barrister Michael Mansfield QC for Hanratty said the original trial was "fatally flawed".

He said this was in "large measure" due to the actions of the senior police officer, who has since died, in covering-up evidence in several key areas.

It was alleged at the time that Hanratty came across the 36-year-old victim, Mr Gregsten and his 22-year-old girlfriend, Valerie Storie, inside a parked Morris Minor in August 1961.

They were confronted by a man with a gun who ordered them to drive to a remote lay-by, where Mr Gregsten was shot dead.

Valerie Storie was raped, shot five times and left for dead. She survived but was paralysed from the waist down.

Hanratty was arrested, tried and convicted for murder.

Alibi query

The jury did not believe his story that he was in Rhyl at the time of the attack - despite the landlady of a B&B backing his claim.

In the years after his execution, numerous witnesses have come forward to support that story.

Valerie Storie: Conviction relied largely on her memory

His conviction was based largely on Miss Storie's recollection of the voice of her attacker.

Mr Mansfield, however, argued over the course of the appeal that she saw him for only a few seconds during the six-hour ordeal, and failed to pick him out of the first police identity parade.

In 1999, the case was referred to the Criminal Cases Review Commission (CCRC), the independent watchdog set up to investigate alleged miscarriages of justice.

After carrying out its own investigation, it sent the case to the Court of Appeal.

But the case took another twist when DNA samples were taken from members of Hanratty's family.

DNA issue

They were checked against samples found on Miss Storie's underwear and a handkerchief wrapped around the murder weapon.

I'm dying tomorrow but I'm innocent - clear my name

James Hanratty

The results showed there was a 2.5 million to one chance that the samples came from someone other than Hanratty.

In March 2001, DNA sample extracted from Hanratty's exhumed body was matched by forensic experts to two samples from the crime scene.

The family believed that the DNA sample could have been contaminated.

Hanratty protested his innocence until his death. On the eve of his execution, he told his family: "I'm dying tomorrow but I'm innocent. Clear my name."

The judges are due to give their judgment, which they reserved at the completion of legal argument on 25 April, at the Court of Appeal in London on Friday afternoon.