A second man, now aged nearly 80, is named as the alleged killer in a petition which has been sent to the Court of Appeal and which is expected to be heard within weeks.
Mattan's seriously ill widow, Laura, aged 68, who married the Somali seaman in Cardiff when she was 17, and her family have campaigned for years for a pardon. Mrs Mattan, who has had several operations for cancer, says she refuses to die until her late husband is pardoned.
The Mattan case is the first to be referred to the Court of Appeal by the Criminal Cases Review Commission, which was set up six months ago to investigate suspected miscarriages of justice.
Mattan, who was executed within a few months of the murder of shopkeeper Lily Volpert in the Tiger Bay area of Cardiff docks, always maintained his innocence.
In 1952, Tiger Bay was a busy, working-class, multi-racial neighbourhood and the murder of Miss Volpert, a 41-year-old spinster, stunned the close- knit community. The killer slit his victim's throat as she opened her shop door then stole pounds 100.
There was no trace of a murder weapon, no motive, no evidence of blood- stained clothing. No forensic tests were carried out. Mr Mattan's conviction rested on the identification evidence of one witness, a police informant with convictions for violence. Specks of blood on a second-hand shoe were later found to be animal blood.
Since then the quest for a pardon for Mattan has become a cause celebre in the modern docklands of the Welsh capital.
Mrs Mattan's son, Philip, who has spent several years investigating the killing, said: "The whole of the docks area was cornered off and ships kept in port. They checked on a number of places including the lodgings Mahmood shared with some men from Jamaica and West Africa because he and my mother could not get a place together.
"Seventeen days later he was arrested for the alleged theft of a raincoat and taken in for questioning, and was then told that the police wanted to talk to him about a more serious matter.
"The original description of the person they were looking for was a tall man of Somali appearance with a moustache, a gold tooth and scars on his face. None of that fitted Mahmood, who was five foot eight. Then 17 days later, Mahmood's name is given to the police and he is arrested. We believe he was wrongly named by a man who wanted to move attention away from him. It is that man who is named in the petition for an appeal."
Mrs Mattan, who married Mahmood in 1945, also remembers exactly where her husband was at the time of the murder. "He was standing on another doorstep across the road and a long way from where it happened," she says.
"He was convinced they would find out they had made a mistake. He couldn't speak very good English, but he kept on saying, 'I kill no woman'. He said they would have to pay compensation to him for false arrest. All the way up to and through the trial I thought that every knock on the door was him coming home to us.
"I still believed right up to the end that they would let him go, but they didn't, they hung him. When they did that I just locked myself away in my room with my kids, and then for some time afterwards I used to think I could see him walking down the street towards me. He was a very good husband and father. All he wanted to do was go to work and he went to sea to earn money until I was having the third child when he said he couldn't go and leave me anymore and wanted to see the boys grow up."
The first attempt at a pardon, encouraged by leaders of Cardiff's large Somali community, was turned down by the then Home Secretary, James Callaghan, nearly 30 years ago. It was not until four years ago that the new campaign began.
Philip Mattan began the campaign to pardon his mother's husband in 1994. "I met a Somali seaman in the docks and he said it was about time we cleared his name. I knew he was executed, but it was never talked about at home while we were children.
"I started digging around in old files and what came out was a very sad story of great injustice. I started a leaflet campaign and the feedback we got was that very few people had ever believed he did do the murder.
"The person who we say did do it has a conviction for a serious offence of violence. What happens to him now if our appeal is successful, I don't know. He is old now and a lot of people are dead so it would be difficult to prosecute him. All we want is a pardon for Mahmood."
The remains of Mahmood were moved from Cardiff Prison to an outside cemetery last year.
The family's solicitor, Lynne De Maid, said: "We haven't had a date yet, but it could be before Christmas. We do name a man we believe responsible for the murder in the petition. He is still living in Cardiff. We are confident, we don't see how anyone can stand up and defend our application. Mahmood was the last person to be hung in Wales and we are advised there will be considerable compensation."Reuse content