Moors murderer Ian Brady has revealed details about where one of his victims, 12-year-old Keith Bennett, is buried, police believe.
Greater Manchester Police said in a statement that the killer had finally disclosed details of the location of the body to one of his long-term visitors to the high-security hospital where he is being detained.
The force added that a 49-year-old woman had been arrested in south Wales on suspicion of preventing the burial of a body without lawful exercise and remained in police custody for questioning.
Brady may have revealed the location of Keith's grave in documents passed to his legal advocate with strict orders they are only to be opened after his death, it was reported.
A Greater Manchester Police spokesman said: "On July 30, 2012, Greater Manchester Police received information that led officers to believe that Ian Brady had recently given details of the location of Keith Bennett's body to one of his long-term visitors.
"Officers in the cold case unit made inquiries to verify the accuracy of this report and have since had extensive contact with Ashworth hospital and Keith's close family.
"As a result, warrants obtained under the Police and Criminal Evidence Act were executed at Ashworth Hospital and a private address in South Wales.
"A 49-year-old woman has been arrested in south Wales on suspicion of preventing the burial of a body without lawful exercise and remains in police custody for questioning. Searches of both locations are ongoing."
A spokeswoman for Ashworth Hospital in Merseyside, where Brady has been detained for the last 25 years, declined to comment, saying it was a matter for the police.
While Brady has revealed where some of his victims were buried, he has always refused to disclose any details about the location of the Keith's body, despite pleas from his family.
His refusal has caused constant heartache for Keith's mother, Winnie Johnson, who has cancer and recently appealed for Brady to break his silence before she died.
Now Jackie Powell, who was appointed the murderer's legal advocate under the Mental Health Act in 1999, said Brady gave her a sealed envelope to pass on to Mrs Johnson in the event of his death.
She told the Daily Mirror: "I received a letter and a sealed envelope which said on the front 'to be opened in the event of my death'.
"He says he doesn't wish to take his secrets to the grave and within the sealed envelope is a letter to Winnie Johnson.
"Within that is the means of her possibly being able to rest."
Brady and his partner, Myra Hindley, who died in jail in 2002 aged 60, were responsible for the murders of five youngsters in the 1960s.
They lured the children and teenagers to their deaths, with victims sexually tortured before being buried on Saddleworth Moor above Manchester.
Pauline Reade, 16, disappeared on her way to a disco on July 12, 1963 and John Kilbride, 12, was snatched in November the same year.
Keith Bennett was taken on June 16, 1964 after he left home to visit his grandmother; Lesley Ann Downey, 10, was lured away from a funfair on Boxing Day, 1964; and Edward Evans, 17, was killed 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 in 1987 to help police find the remains of the missing victims but only Pauline's body was found.
Mrs Johnson has made repeated calls for Brady to reveal the location of his grave.
Last December she said she wanted to hear face-to-face from Brady where her son was buried.
And in July she renewed her plea, saying in a letter to the killer that her dying wish was to know where Keith's body was.
Brady, 74, was due to go before a mental health tribunal in July, but it was delayed after he suffered a seizure.
The tribunal was to consider his application to be transferred to a Scottish prison and be allowed to die. He has been tube-fed since refusing food 12 years ago.
But last month Mrs Johnson's solicitor said she would not be attending the hearing as it would be "too traumatic" for her.
John Ainley, senior partner at North Ainley Halliwell, said that Mrs Johnson was in hospital and not well enough to attend.
He said: "In any event, it would be too traumatic for her to have any involvement in a hearing that deals with Ian Brady.
"Winnie has made it perfectly clear over the years that she considers Ian Brady should remain in a mental hospital for the remainder of his natural life and not be transferred to a prison either in England or Scotland.
"Presumably, the intention would be to go on hunger strike with a view to ending his own life. She does not consider this should be his prerogative."
Mr Ainley said his client still wanted answers from Brady.
He said: "She has only one question to ask Ian Brady, that is 'Where is my son Keith?'
"She is convinced that he could, if he wished, provide this information.
"Her one and only desire is to give her son a proper family burial during her lifetime. Nothing short of that will ever give her peace of mind."
The solicitor said Mrs Johnson was "not in the best of health" and that she was not well enough to deal with the pressures - including the media interest - surrounding the tribunal, which was due to be held in public.
On Wednesday The Sun reported that Mrs Johnson was being cared for in a hospice.
The newspaper quoted her son Alan Bennett as saying: "Winnie is going in to a hospice for about two weeks.
"She can be closely monitored and get the correct form of pain relief that is needed for when she returns home."