A solicitor who used to represent Winnie Johnson, Keith Bennett's mother, has described the latest development as "extremely interesting and exciting".
David Kirwan, a managing partner with Kirwans law firm, said he had a series of face-to-face meetings with Ian Brady at Ashworth mental hospital in 2007. He said:
There is potential credibility to the claim that Brady may have written such a letter. I believe it is a human instinct not to take secrets to our grave.
I believe Ian Brady knows the exact whereabouts of Keith Bennett's grave and iscapable of directing police to it.
However, it is important to remember who we are dealing with and how he seems to enjoy bizarre mind games and manipulation.
During interviews Brady told me mischievously how when he was on the moors with the police in 1986 he walked them across the graves of his victims.
Police first became aware of the possible existence of a letter from Ian Brady his victim's mother in late July, ITV News can reveal
Keith Bennett's brother speak out over body claims
Jackie Powell was detained in south Wales on suspicion of preventing the burial of a body without lawful exercise.