Cruel killer Brady taunted the brother of Moors murder victim Keith Bennett with the letter in 1991.
The contents of the twisted note have now been revealed, after police were refused permission to go through Brady’s belongings.
In the evil child killer’s note, Brady said to Keith’s brother Alan he would give the details of the burial site and the family should stop looking for it.
He wrote: “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.”
However, the promised clues never came.
The Bennett was hopeful of finally getting the information after Brady died aged 79 at Ashworth Hospital in Merseyside, in May 2017.
In his final hours the killer who attacked and murdered children with girlfriend Myra Hindley asked for two locked suitcases he had with him to be put into secure storage.
The family believes this may be where the clues are hidden.
But police were refused a warrant to search them.
Robert Makin, Brady’s solicitor has also denied a plea by police and Keith’s family to examine the mystery cases.
Keith, 12, was snatched on his way to his grandmother’s house on June 16, 1964.
Evil Brady and Hindley killed Keith along with at least four other children in and around Manchester in the 1960s.
Other victims have been found on Saddleworth Moor after the sick pair took photographs of themselves near the graves.
But Keith was never found.
Neither Brady nor Hindley revealed their final victim’s resting place, triggering a search that has lasted decades.
Alan, 62, told the Manchester Evening News: “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.
“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 added: “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.”