Ian Brady sent a letter to the brother of Moors murder victim Keith Bennett saying he would leave 'special instructions' of how to find the child's remains in his will.
The taunt from the killer filled Keith's family with hope, but they never received further clues from him.
In the letter sent to Keith's brother, Alan Bennett, in 1991, Brady writes: 'I again advise you to stop searching until matters are resolved. My will contains special instructions for you alone. My time is almost over.
'Sincerely, Ian Brady.'
As the contents of the letter were revealed for the first time on Friday, Alan said: 'It would be another 26 years after he sent that letter before he died. At the time we were hopeful that it might lead to Keith.
Keith Bennett was one of five children murdered by Ian Brady (left) and Myra Hindley between 1963 and 1965.
'I wrote to him several times and at one point asked if he would correspond with John Stalker (former assistant chief constable) after he left GMP, so that information could be passed that way. But Brady would change the subject, and nothing came of it.'
Alan fears it could be a twisted game Brady was playing, but he also wonders if the 'special instructions' might be in two locked briefcases held by Brady's solicitor.
Alan believes they could contain clues as to the exact spot that Brady and Myra Hindley buried Keith, after abducting and killing him in 1964.
But Brady's solicitor Robin Makin has refused to give the cases to Cold Case Unit officers from GMP.
Just before his death in May 2017, Brady requested the two combination-locked cases be put in secure storage.
It has now emerged officers went to court for a search warrant to open the cases to check them for clues.
But a district judge refused the application, stating there was no prospect of an investigation leading to a prosecution as both killers were dead.
Keith's brother, Alan, 62, said: 'There is a desperate need to look for anything that may help in the recovery of Keith's body and there may be something in those cases. We cannot be sure be we need to know for sure - one way or another.
Alan Bennett, brother of Moors Murder victim Keith Bennett
'During my correspondence with Brady many years ago he stated that he had left instructions in his will for me alone. He did not give any further detail but it was at a time when I was searching on the moor and asking him about routes taken, areas of the moor, landmarks etc.
'The refusal by Mr Makin to help any further is a great cause of distress considering that my brother's body still remains on the moor while all the other victims have been returned to their loved ones for a proper burial.'
Alan spent the best part of decade searching Saddleworth Moor himself around Shiny Brook stream with a team of helpers digging through peat for Keith's remains. His and Keith's mother, Winnie Johnson, who died in 2012, also visited the moors in a vain search.
Jonathan Reynolds, the MP for Hyde, earlier said: 'Greater Manchester Police believe that there's a possibility, I'll say no more than that, that there is something of interest to them in those possessions.
'The historic correspondence with the family appear to validate that. So, isn't the best way forwards for the police to be given access to those possessions so they can settle the issue once and for all. What the Bennett's have been through is unconscionable if we can make things a tiny bit better, surely that's the right thing to do.'
Left: An artist's impression of Moors Murderer Ian Brady. Right: Keith Bennett, 12, who was snatched and murdered by Brady and Hindley in 1964
Mr Makin, of E Rex Makin & Co Solicitors in Liverpool, declined to comment on Alan's plea to hand over the briefcases to GMP.
But speaking after Brady's death in 2017, Mr Makin said: 'If Keith Bennett's body was going to be found with his assistance that would have happened in the 1980s and I just don't think he had any really compelling new information about where his body was located that would have assisted in finding it. I may be wrong, but that's my view.'
He also said: 'The will does not contain any instructions for Alan Bennett or contain anything that could be given to him that would now identify where Keith Bennett's body was buried.'
But it is understood Brady made more than one will.
Keith was one of five children murdered by Brady and Hindley between 1963 and 1965.
He was 12-years-old when he set out on his way to his grandmother's house in Longsight on June 16, 1964.
Keith's mum, Winnie Johnson, waved him off as he crossed Eston Street. She would never see him again.
A short time later, just off Stockport Road, Hindley wound down the window of her new Mini and asked Keith if he would mind giving her a hand with some boxes. Brady was sitting in the back of the car.
In 1986 after Hindley and Brady had confessed for the first time to killing Keith and Pauline Reade, a new search of the moors was carried out by GMP.
The body of Pauline, who was 16 when she was killed in 1963, was found on July 1, 1987. But after Pauline's remains were found the search for Keith's was stopped.
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