Winnie Johnson said in her final interview that she feared Moors Murderer Ian Brady would never reveal the whereabouts of her 12-year-old son's body in a "final sick twist".
The mother of Keith Bennett fought tirelessly for decades to find him and provide a Christian burial but Brady always refused to tell her where he buried him on Saddleworth Moor above Manchester.
She died peacefully in a hospice in the early hours of Saturday morning, aged 78, having suffered from cancer for a number of years.
Her family has now vowed to continue her campaign. Brady has been urged to "do the decent thing" and finally tell them where the body is so that Keith can be given a Christian burial.
The closest Winnie came to giving him a funeral 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."
In an interview with The Sun, conducted from her hospital bed, she had said: "I don't know now if Brady will ever tell me where my Keith is buried.
"He could take it to the grave with him. I suppose that would be his final sick twist. Or he could give me hope like he has done before and then nothing would come of it."
She said it would make her feel "on top of the world" to know where her son's body was, and added: "It would mean my dying wish had come true and we had finally got Keith home. I don't give a s*** about Brady any more. I am running out of time and just want to bring my son home."But I feel in my heart he won't ever tell me."
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.
Brady's mental health advocate, Jackie Powell, told a Channel 4 documentary - due to be screened tomorrow 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.