In its ruling, the Sixth Circuit Court of Appeals essentially restated its original argument from 2005 - that Richey was inadequately defended at his original trial, in violation of the Sixth Amendment of the Constitution. The justices were, however, forced to enter into lengthy legal justifications to overcome objections from the Supreme Court in Washington, which unexpectedly intervened in the case last time around.

Richey's lawyers and friends, along with Amnesty International, hailed the ruling as a key victory for a man they believe to be innocent of the crime for which he was convicted.

It is not clear, however, whether Ohio prosecutors will now give up, go back to trial, or send the case back to the Supreme Court for a new appeal.

Richey was 21 years old when he was arrested in 1986 and accused of being criminally responsible for the death of his ex-girlfriend's two-year-old daughter, who perished in a fire just a few days before Richey was due to go back home to Scotland.

Prosecutors said he deliberately set the fire in a jealous rage aimed at the girl's mother and her new boyfriend. The victim, Cynthia Collins, died when the fire raged out of control, they contended.

Richey says he has no memory of what happened that night because he was drunk. However, numerous experts have come forward to challenge the theory that the fire was deliberately set by anyone. The firefighters who rushed to the scene in 1986 said that Richey made strenuous efforts to save the baby - they had to hold him back to make sure he did not burn to death himself.

For Amnesty and other campaigning groups, the case has been a prime example of the failings of the US system of criminal justice, especially where the death penalty is involved. Mr Richey refused a plea bargain that would have spared him the execution, because he did not want to admit guilt for a crime he says he did not commit.

On 13 separate occasions he has been given an execution date - one of which was postponed just an hour before he was scheduled to be put to death. He has suffered three heart attacks in the past five years, the most recent last August.

Amnesty International's director in Scotland, John Watson, said of the latest appeals ruling: "This is fantastic news and represents the opportunity that Kenny has long fought for - the chance to clear his name in a proper trial ...

"On the one hand it is disturbing that it has taken this long for Ohio to look again at Kenny's case, but now at least Kenny may be on the road to release."

Karen Torley, an anti-death penalty campaigner who grew so close to Richey that she is now engaged to him, was equally delighted. "I have always had full confidence in the fact that Kenny is absolutely innocent," she said, "and now Kenny's now one vital step closer to proving that to the world."