Paddy Nicholls, 69, will be cleared at the Court of Appeal on Friday after new evidence showed that the woman he was convicted of killing most likely died of natural causes.
The Independent has learned that Mr Nicholls' appeal will not be contested by the Crown. His 23-year prison term is by far the longest to be served by a person wrongly convicted. He could have been released earlier, but has always refused to admit his guilt.
Mr Nicholls said yesterday that he felt "sad" and "extremely bitter" that he had spent more than a third of his life in prison for a crime he did not commit.
He was released on bail in March following the presentation of new evidence rubbishing the original pathologists' conclusions that the "victim", Gladys Heath, had been beaten and suffocated.
Mr Nicholls was convicted of the murder of Mrs Heath, a 74-year-old family friend, whom he found slumped on the floor of her home in Worthing, Sussex, in 1975. She had suffered a stroke and had recently had a toe amputated.
He always maintained that he found her in that condition, but two pathologists - Dr Hugh Johnson and Professor J M Cameron, both now dead - concluded that she had died of a heart attack after being suffocated and severely beaten about the face.
However, a review of the evidence by Professor John Crane, an Irish state pathologist, in a report to the Criminal Cases Review Commission, concluded: "I cannot agree with either Dr Johnson or Professor Cameron that this woman sustained severe facial injuries as the result of an assault.
There is no evidence ... that suffocation played a part in her death." A key prosecution witness who testified Mr Nicholls had admitted his guilt in prison later retracted his statement, admitting he had lied.
Mr Nicholls told The Independent: "I have had a terrible time trying to cope with things since I got out. I feel extremely bitter and sad. It was 23 years of my life. You try and do your best in life, but now I have nothing." Mr Nicholls will be entitled to compensation expected to total hundreds of thousands of pounds. Previously the longest serving victim of a miscarriage of justice was Judith Ward who spent 18 years in jail for an IRA bombing she did not commit.Reuse content