The family of the mother of Moors Murders victim Keith Bennett has vowed to continue the fight to find his body and give her son a Christian burial.
Winnie Johnson, 78, died in the early hours of Saturday at a hospice following a long battle against cancer.
Glaswegian Ian Brady, the killer of her 12-year-old son, has always refused to say where he buried him on Saddleworth Moor above Manchester despite decades of pleading from his victim's grieving mother.
She also passed away not knowing about fresh reports that Brady may have detailed the location of the body in a supposed letter addressed to her to be opened on his death.
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 never to be found.
In a statement, Winnie's family said: "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."
Her lawyer John Ainley said Brady still held the key to finding the burial spot.
"Despite her personal appeals directly to Brady and via my office, Brady had persistently ignored the wishes of a grieving mother," he said.
"She has died without knowing Keith's whereabouts and without the opportunity to finally put him at rest in a decent grave.
"It is a truly heartbreaking situation that this opportunity has now been irrevocably lost."
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 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.
Keith Bennett was snatched after he left home in Longsight on his way to his grandmother's nearby house on June 16 1964.
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.
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 to help police find the remains of the missing victims but only Pauline's body was found.