London (CNN) -- The mother of a victim of one of Britain's most notorious killers died Saturday, a day after police said they were investigating a possible clue to where her child was buried nearly 50 years ago.
Winnie Johnson, whose 12-year-old son Keith Bennett went missing in 1964 in northern England, had spent the long decades since seeking first to find, and then to give a proper burial to, her murdered child.
But her death after serious illness has come before that hope could be realized.
Ian Brady, who was jailed for life in 1966 for three other child murders committed with the help of his partner Myra Hindley, admitted killing the boy in 1987 but has never disclosed the whereabouts of his body.
The other four victims were buried on Saddleworth Moor, a lonely upland expanse in the Pennine hills, near Manchester, but repeated searches have never uncovered Keith's remains.
Brady, known as the "Moors Murderer," remains in a secure psychiatric unit.
A statement on the family's website, Searching for Keith, confirmed that Johnson, a "much-loved mother, grandmother and great-grandmother," had died at age 78.
"Winnie fought tirelessly for decades to find Keith and give him a Christian burial," it said.
"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."
Police revealed Friday that they were investigating claims that Brady may recently have given details of the burial spot to one of his longtime visitors, in a sealed letter to be passed to Johnson after Brady's death.
The information came to light when a documentary filmmaker interviewed a woman who has been acting as Brady's mental health adviser, the Press Association news agency reported.
Martin Bottomley, head of Greater Manchester Police's cold case review team, cautioned Friday against leaping to conclusions but said police were taking the possibility Brady had written such a letter seriously.
"We do not know if this is true or simply a ruse, but we clearly have a duty to investigate such information on behalf of Keith's family," he said in a statement.
"Since Keith was so cruelly taken away all those years ago, our thoughts have always been with his family as they try to come to terms with what happened. All they want is to finally be able to lay Keith to rest."
A 49-year-old woman was arrested in South Wales on Thursday on suspicion of preventing the burial of a body without lawful exercise, and has been released on bail pending further inquiries, the police statement said.
Documents have also been seized from the address and are being examined, police said.
Brady and Hindley were taken by police to Saddleworth Moor to look for the bodies of Bennett and another victim, 16-year-old Pauline Reade, after they admitted those killings in 1987, the Press Association said. However, only Reade's remains were found.
The lawyer who represented Johnson, John Ainley, said it was a "heartbreaking situation" that she had died without ever learning where her son was buried.
"Over the years and in all our personal meetings, Winnie has insisted Brady is the only person who could put her mind at rest and give her the chance to give Keith a decent burial before she passed on," he said, according to a statement from the law firm.
"She was convinced Brady knew where her son was buried and she told me she wanted the search to continue to find Keith."
Johnson is quoted on the Searching for Keith website as saying: "My greatest hope in this life from the day he left is to have him home, I now accept he is not alive but I still believe I have the right as his mother to give him a Christian burial."
CNN's Susannah Palk contributed to this report.