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 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 him on Saddleworth Moor above Manchester so Keith can be given a Christian burial.
The closest Winnie Johnson 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."
Writing on his website, searchingforkeith.com, Mr Bennett, who was nine when his brother was taken off the street by Brady and 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.
"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."
Her death comes amid a police inquiry 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 tonight, the Moors Murderer gave her a sealed envelope containing a letter to pass to Mrs Johnson when he died.
Ms Powell, 49, was arrested on Thursday on suspicion of preventing the burial of a body without lawful exercise, but was bailed pending further inquiries.