Myra Hindley formally petitioned the Government to allow her to be hypnotised in the hope that it would help locate the body of Keith Bennett, it emerged.

The letters from Hindley to the then Home Secretary Douglas Hurd were among thousands of documents in 600 files on the Moors Murderer made public today at the National Archives.

In one letter dated December 11, 1987, Hindley wrote from her prison cell: “I now wish to urge you to reach a positive decision [on hypnosis] and grant the request.

“If the proposed hypnosis is unsuccessful, at least it can be said that everything humanly possible has been done.

“If it is successful the immeasurable relief it will bring to Mrs Johnson [Keith’s mother], the fact that the police can finally close the file on the whole case, and the benefit to society knowing at last that the Moors case, which has haunted the psyche of the nation, is finally resolved and exorcised, will be no small matter.”

The letter followed a formal petition filed by Hindley two months earlier. She was prepared to bear the full cost of the hypnosis herself and determined that even the smallest of details uncovered through the process could prove pivotal to the case.

Keith Bennett was just 12-years-old when he became the third victim of Hindley and Ian Brady in 1964. His body was buried on Saddleworth Moor outside Manchester and is the only body that has never been recovered.

In a prison report from Cookham Wood, where Hindley served much of her life sentence, a staff member wrote: “One of [Myra’s] greatest regrets is, I believe, not being able to remember the whereabouts of the last child, and thereby not allowing him or his family to ‘lie in peace’ at last.

“Myra ‘lives’ with her offences far more than any inmate I have ever known.”

Among other information that emerges from the files are details about Hindley’s struggles with fellow inmates-turned-informers who sold her out to the press, her declining health and her complicated relationship with Brady.

In an exchange of brief letters between staff at her prison and Brady’s, it emerges that the couple broke up in 1972 with a bookmark that Hindley had sent to Brady for Christmas the year before.

A letter dating July 1972 read: “Brady asked that [the bookmark] be returned to Myra. It’s obviously a symbolic gesture meaning the relationship is at an end.”

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