DETECTIVES suspect World's End killer Angus Sinclair may have been involved in the murder of a woman for which another man was jailed.

Retired police officers who worked on the investigation which eventually snared the 71-year-old for the murders of Helen Scott and Christine Eadie in Edinburgh also think he was behind the death of Glasgow woman Frances Barker.

The 37-year-old disappeared from outside her home in Maryhill, and her body was later found in Glenboig, Lanarkshire.

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A man named Thomas Ross Young was eventually jailed for her killing, but has always protested his innocence. He died while waiting to hear if his case could be appealed.

But now a BBC documentary 'The Forgotten Women' - produced by Caitlin Smith and presented by Edi Stark - has alleged he may have attracted mistaken suspicions because he was already known to be a prolific sex offender and was also the main suspect in the murder of 17-year-old Patricia McAdam, which remains unsolved to this day.

The murder of Frances Barker was re-examined by officers working on Operation Trinity, the cold case investigation launched in 2004 which eventually led to Sinclair's conviction for the World's End killings.

Sinclair has only been tried in court for the deaths of Helen Scott and Christine Eadie, but the officers say strong circumstantial evidence links him to the murders of Glasgow women Hilda McAuley, Agnes Cooney and Anna Kenny, all in 1977.

Retired Det Chief Supt Eddie McCusker, who led the Strathclyde Police team on Operation Trinity, said: "Since my first engagement to this day, the names of the women have been imprinted on my mind and I have certainly not forgotten them.

"I feel a huge sense of frustration there has been no resolution to their cases.”

He added: "These four women were murdered by Angus Robertson Sinclair. I have no doubt about. I include Frances Barker."

Frances Barker's name was added to the list of Sinclair's potential victims after officers pored over the case logs of more than a cases of violent murder cases across Scotland around the time Sinclair was known to be operating.

Six were found to have been killed in exactly the same fashion. They were abducted, often from a public place, taken to a rural location where they were bound with items of their own clothing and raped, before being strangled.

Those women were Helen Scott and Christine Eadie, Hilda McAuley, Agnes Cooney and Anna Kenny - and Frances Barker.

Officers were also able to establish that Sinclair lived in Maryhill Road - the location where Frances Barker was last seen alive - and also fished in Glenboig, where her body was eventually discovered.

At the time, Thomas Ross Young was the prime suspect in her death because of his violent past and because he lived in the area.

Officers had investigated him for Patricia McAdams death, and were able to prove she had been in his cab but not that he killed her as her body has never been found.

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He was convicted after items belonging to Frances Barker were found in his home, but Mr McCusker has doubts about the evidence.

He said: "Given that Thomas Ross Young I believe was innocent, then how the items got to where they were found is matter for speculation."

Forgotten Women airs on BBC Radio Scotland today (WEDNESDAY) at 1.30pm.