THE estranged wife of Angus Sinclair worked with detectives in a bid to help bring her husband to justice for the World's End murders.

Sarah Hamilton, 64, spent a year secretly helping police investigating the man who has now been convicted of four killings and is thought to be responsible for up to six more.

She worked closely with officers piecing together a case against her husband after he was cleared of murdering teenagers Christine Eadie and Helen Scott in 1977 following the collapse of an earlier trial. Her input included writing letters to Sinclair with the help of police in the hope he might make an incriminating slip-up or confess. However, police said he never took the bait.

Sinclair, 69, was jailed for a minimum of 37 years at the High Court in Livingston last Friday after being found guilty of raping and murdering of Ms Eadie and Ms Scott.

Sinclair met the 17-year-olds during a night out at the World's End pub in Edinburgh. Their bodies were found on a beach and in a field in East Lothian the next day. Ms Hamilton also aided police before the failed trial in 2007.

Throughout the second trial Sinclair blamed Ms Hamilton's late brother, Gordon Hamilton, for the teenagers's deaths.

Sinclair was 25 when he married Ms Hamilton, from Townhead in Glasgow, in 1970 in the registrar's office in Leith. She was 20 and a trainee nurse. Her brother was 15.

A senior police source said: "She was a young student nurse when he she met him. She could be seen as a kind of victim.

"He is calculating and manipulative. She never knew what he was up to. We were part of her life for about a year. She went through the mill to help to the extent she wrote letters to him trying to get him to confess."

Sinclair killed for the first time when he was 16, served six years for the culpable homicide of his eight-year-old neighbour Catherine Reehill in Glasgow.

Ms Hamilton, now thought to be living in Gloucester, told Sinclair's first trial that her husband had admitted well into their marriage that he had killed Catherine but managed to convince her he had "made a mistake".

She told The Herald after the earlier trial: "That was a horror to me. I thought that I knew him. I looked at my brothers and other people in my life. They had all made mistakes; we all do when we're young."

Two years after they married, the couple had a son, Gary, now 42.

Ms Hamilton left her husband before he was jailed for life in 1982 after pleaded guilty to the rape or sexual assault of 11 children aged between six and 14.

In 2001, following advances in DNA technology, Sinclair was convicted of the 1978 murder of 17-year-old Mary Gallacher from Glasgow. Last week he was convicted of his third and fourth killings following a change to the double jeopardy law which had meant no-one could be tried twice for the same crime.

It has also been suggested that Sinclair may have been responsible for the murders of Anna Kenny, 22, Hilda McAuley, 36, and Agnes Cooney, 23, and Frances Barker, 37, in 1977; Eddie Cotogno 63, the following year; and Helen Kane, 25, whose body was found on a hill overlooking Holyrood Park in Edinburgh in 1970.

Another man, Thomas Young, as convicted of killing Ms Barker. He died in prison earlier this year.

Police Scotland confirmed Ms Hamilton "would have been spoken to as part of that inquiry". She could not be contacted yesterday.