Ian Brady has been told by the family of Keith Bennett to "do the decent thing" following the death of Bennett's mother, Winnie Johnson.
The Moors Murderer has steadfastly refused to reveal the whereabouts of her 12-year-old's body, but following the death of Johnson, the family has urged the killer one last time to reveal the secret.
The mother of Keith Bennett fought tirelessly for decades to find him and provide a Christian burial but Brady has always refused to tell her where he buried him on Saddleworth Moor above Manchester.
The closest she came to giving him a funeral, amid her loathing of Brady, was to hold a memorial service at Manchester Cathedral two years ago in which she tearfully told the congregation: "I'm Keith's mother ... he's there on the Moors, I want him back."
She died peacefully in a hospice in the early hours of today, aged 78, after she had battled cancer for a number of years.
Brady, 74, and his partner, Myra Hindley, who died in jail in 2002 aged 60, were responsible for the murders of five youngsters in the 1960s.
Most of their victims were sexually tortured before being buried on Saddleworth Moor, with Keith's body the only one yet to be found.
Keith was snatched after he left home in Longsight on his way to his grandmother's house nearby on June 16 1964.
In a statement, Winnie's family said today: "She was a much loved mother, grandmother and great-grandmother, and is survived by one younger brother.
"Winnie fought tirelessly for decades to find Keith and give him a Christian burial. Although this was not possible during her lifetime, we, her family, intend to continue this fight now for her and for Keith. We hope that the authorities and the public will support us in this."
Martin Bottomley, head of investigative review of Greater Manchester Police's major and cold case crime unit, paid tribute to Winnie for spending the majority of her life "courageously fighting to get justice for Keith".
"All she wanted was to know where Keith was buried so she could lay him to rest," he said.
"There is only one person who knows where Keith is buried and that is Ian Brady himself. I would implore him at this extremely sad time and knowing that Winnie has died not knowing where Keith is buried to at last do the decent thing and tell us where he is."
Her lawyer, John Ainley, is sceptical about whether Brady will finally come forward with information.
"One would think that now Winnie is no longer here and the family are so desperate to get this information, that the least he (Brady) could do is to volunteer valid information that would throw some light on Keith's whereabouts," he said.
"I am not quite sure that is going to happen."
Her former solicitor, David Kirwan, said Brady was "a control freak with such a venomous hatred of the authorities, any clues he provides will be in riddle form".
He added: "He thinks he is cleverer than everybody else, thinks he is superior to everybody else."
Jean Taylor, the founder of campaign group Families Fighting for Justice, who knew Winnie, said killers like Brady had to have control.
Her daughter Chantel was killed in 2004 in Birkenhead, Merseyside, and Mrs Taylor was anguished at not being able to provide a proper burial
"They get off on knowing because they get self-gratification as Brady did," she said.
"To deny a family the right to a burial is beyond justice, there's no justice, but I never thought Brady would disclose where the body was."
The whereabouts of Keith Bennet's body remains unknown
Marie McCourt, of Billinge, Wigan, who is still searching for her daughter Helen's body's almost 25 years after she was murdered, said she feared the same fate as Winnie.
She said: "Her death does take her away from that whip that Brady keeps using, it takes away his manipulation tool he has used over the years.
"I hope he suffers a lot for it now.
"He has lost his bargaining tool and I hope people stand up to him now."
Her death comes amid a police investigation into whether a letter exists in which Brady apparently discloses the location of Keith's body.
Brady's mental health advocate, Jackie Powell, told a Channel 4 documentary - to be screened on Monday night - the Moors Murderer gave her a sealed envelope containing a letter to pass to Winnie Johnson in the event of his death.
That information was passed to police and Ms Powell, 49, was arrested on Thursday at her home in Llangennech, South Wales, on suspicion of preventing the burial of a body without lawful exercise.
Ms Powell, who is also an executor to Brady's will, was later released on bail pending further inquiries. It is understood she claims she returned the sealed envelope to Brady before her arrest.
Detectives examining a large number of documents seized have so far found no letter or any evidence to suggest Brady has disclosed the location of Keith's body.
A search of Brady's quarters at Ashworth Hospital in Merseyside, where he has been detained since 1985, has also failed to uncover the alleged letter.
Brady was due to go before a mental health tribunal last month, 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.
No new date has been set for the hearing in Manchester but it is not thought to be imminent.
The other victims of Brady and Hindley were Pauline Reade, 16, who disappeared on her way to a disco on July 12 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 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 to help police find the remains of the missing victims but only Pauline's body was found.