Keith Bennett will remain "in the possession" of Moors murderers Ian Brady and Myra Hindley until his body is found, the victim's brother has said.
Alan Bennett said the death of his mother, Winnie, 78, on Saturday must not be seen as closure to the case as the family vowed to continue the fight to locate the remains of the 12-year-old.
Brady, 74, has been urged by police to "at last do the decent thing" and finally tell them where he buried Keith on Saddleworth Moor above Manchester so he can be given a Christian burial.
The closest Mrs Johnson came to giving him a funeral was to hold a memorial service at Manchester Cathedral two years ago at which she tearfully told the congregation: "I'm Keith's mother ... he's there on the Moors, I want him back."
Writing on his website, www.searchingforkeith.com, Mr Bennett, who was nine when his brother was taken off the street by Brady and the late Hindley, said: "As far as I am concerned, until Keith is found then he is still in the possession of Brady and Hindley.
"Our fear as a family is that now my mother is no longer with us, this may be seen by the police and the media as some sort of closure to the case. This must not be allowed to happen both out of respect for Keith and my mother's memory and for those of us who loved them both."
His mother's 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 Mrs 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. Detectives are examining a large number of documents and have searched Brady's quarters at Ashworth Hospital in Merseyside, where he has been detained since 1985, but failed so far to uncover the alleged letter.