Moors murderer Ian Brady's mental health advocate will not be charged over allegations she failed to tell the police about a letter which may have revealed where one of his victims was buried, the Crown Prosecution Service said.
Jackie Powell was arrested on suspicion of preventing the lawful burial of Keith Bennett after she told a television documentary that Brady had given her a sealed envelope to pass to Winnie Johnson, Keith's mother, in the event of his death.
The letter was never found and Mrs Johnson died last August still not knowing where her son was buried.
John Dilworth, head of the CPS North West Complex Case Unit, said: "After careful consideration, we have decided that Ms Powell should not be charged, as it cannot be established that she knew the contents of the letter referred to, that the letter in question existed or what information it might have contained.
"The only evidence of the letter's existence was in comments given by Ms Powell to an interviewer and she stated only that she believed it may contain information about Keith Bennett."
Mr Dilworth said: "The only offence that might have been committed by Ms Powell was preventing a lawful and decent burial.
Keith Bennett was murdered in June 1964 by Brady and Myra Hindley
"It is possible to prosecute a person for preventing a lawful burial through a failure to act, but there must be sufficient evidence to prove that the suspect either prevented the burial or intended to do so when they chose not to act."
He added: "Even if it could be proved that this letter existed, there is no evidence to suggest that Ms Powell ever knew the nature of its contents and there is insufficient evidence to prove that she genuinely believed it contained the information in question.
"As such, it could not be established in court that Ms Powell either prevented Keith Bennett's burial or intended to do so.
"We understand that this is still a very sensitive matter for the relatives of Keith Bennett.
"We have written to Keith Bennett's brother to explain our decision and have offered a meeting to discuss this matter."
Martin Bottomley, head of investigative review in Greater Manchester Police's major and cold case crime unit, said: "As soon as we were made aware of the existence of this alleged letter, we made exhaustive attempts to obtain it to establish whether or not its contents would assist us in finding Keith's body.
"That resulted in the warrants we carried out in the South Wales area and at Ashworth Hospital in August 2012.
"However, despite seizing numerous documents and a search of Brady's cell, no such letter has been recovered.
"That in itself does not prove or disprove the letter's existence. It might have been destroyed, it might be hidden elsewhere, it may be in someone else's possession, or it may simply never have existed in the first place and this has been yet more mind games by Brady.
"What I can say for certain is that we have not recovered the letter itself nor any credible information that would help us find Keith."
Mr Bottomley added: "As a result, we have liaised with the Crown Prosecution Service who have concluded there is no realistic prospect of any criminal conviction and therefore no further action will be taken against the woman we arrested.
Keith's mother Winnie died in 2012 never knowing where her son's body lay
"I do want to make this point however: this whole episode about the letter came at a time when Winnie was sadly in her final days.
"Winnie and the rest of her family have suffered unimaginable torment.
"Keith still has surviving relatives who deserve to know the truth and Greater Manchester Police will continue to act on any credible evidence to bring this torment to an end."
Winnie Johnson died last August just days after the revelations about the letter emerged ahead of the Channel 4 documentary.
Tormented to the last after a lifetime of campaigning, the 78-year-old died without fulfilling her wish to find her son's makeshift grave on Saddleworth Moor and give him a proper Christian burial.
Ian Brady and Myra Hindley abducted and murdered the 12-year-old in 1964, the only one of the five young victims whose body has never been found.
A privately funded search on the rocky moors in 2010 failed to find Keith's body
At her funeral service at St Chrysostom's Church, in Victoria Park, Manchester, where Mrs Johnson, a widow, was a regular parishioner and Keith attended Sunday school, the names of her son's killers were never uttered once.
Instead her family, friends and ordinary members of the public among the mourners heard tributes to a courageous mother who battled on despite a life touched by tragedy.
Keith was lured into Hindley's car after he left home in Longsight on his way to his grandmother's house nearby in June 1964.
The other victims of Brady and Hindley were Pauline Reade, 16, who disappeared on her way to a disco in July 1963; John Kilbride, 12, who was snatched in November the same year; Lesley Ann Downey, 10, who was lured away from a funfair on Boxing Day 1964, and Edward Evans, 17, who was axed to death in October 1965.
Brady was jailed for life at Chester Assizes in 1966 for the murders of John, Lesley Ann and Edward.
Hindley was convicted of killing Lesley Ann and Edward and shielding Brady after John's murder, and jailed for life. In 1987 the pair finally admitted killing Keith and Pauline.
Both were taken back to Saddleworth Moor to help police find the remains of their victims but only Pauline's body was found. Brady claimed he could not remember where he had buried the boy.
In 2009, police said a covert search operation on the moor which used a wealth of scientific experts had also failed to discover any trace of Keith.
Brady was due to go before a mental health tribunal last year, but it was delayed after he suffered a seizure.
The tribunal was to consider his application to be transferred to a prison and be allowed to die. He has been tube-fed since refusing food 12 years ago.
The re-listed hearing is due to take place in Manchester in June.