It was not a good summer for Ian Brady.

First, the Glasgow-born serial killer had a seizure and cracked vertebrae. Then his mental health advocate, Jackie Powell, told Channel 4 he had given her a letter which could reveal the location of Keith Bennett, the Moors Murders victim whose body is still buried out on Saddleworth.

All hell broke loose. Police hauled Powell in for questioning and turned Brady's cell over, looking for the letter. Brady was vilified as a sinister Svengali, fiendishly directing events from his cell. And Channel 4 got a heap of publicity for its programme, Endgames of a Psychopath.

Now Brady has written a letter from Ashworth claiming to set the record straight. Powell's letter, he says, never existed. And he, far from being some Machiaevelli toying with a grieving mother, can no longer say exactly where Keith's body is.

"Since 1985 I have repeatedly stated that I know/knew the whereabouts of Keith Bennett," he writes, "but to know or have known the whereabouts is entirely distinct from stating that a vast wilderness that changes with the seasons every year would, after 50 years, remain precisely familiar to anyone."

Why, I wondered, would Brady take the trouble to set out what is basically a history of the major events in his life since imprisonment? But then he has always been a stickler for getting the facts right, as he sees them.

At the end of the Moors Murders trial in 1966, the judge asked him if he had anything to say. "No," he said, "except the revolvers were bought in 1964."

His obsessive planning and passion for detail helped convict him, when notebooks with incriminating evidence were found in a station locker, but the irony is that few today believe a word he says. It's as if the label of serial killer necessarily entails one of liar as well. And when Keith's mother, Winnie Johnson, died without knowing where her son was, the Moors Murderer was confirmed in the public's eyes as a heartless monster.

The claim clearly irks him. In his three-page handwritten letter, Brady criticises Peter Topping's conduct of the 1987 search on Saddleworth, saying he was distracted by thoughts of the book he intended to write. He accuses Manchester Police of bungling and claims he has been offering to return to the moors for Yorkshire Police ever since his last visit, but that they don't want to upset their neighbouring force, or spend public money on going back up there.

"My offer to assist a fresh search for KB [Keith Bennett] came to nothing, as three fields of vested interest were opposed; (a) the Manchester Police did not wish the Yorkshire to succeed where they had failed; (b) the Yorkshire wished to avoid both conflict with Manchester and additional public expense; Ashworth admin, exposed as criminal and corrupt by every public enquiry, wished to avoid all public scrutiny, by keeping me isolated and silent."

Ashworth responded by saying: "Issues relating to enquiries and investigations relating to Keith Bennett are a matter for Greater Manchester Police, not Mersey Care NHS Trust". Greater Manchester Police declined to comment.

A spokesman for West Yorkshire Police denied any conflict of interest. "If we had any information that would support our colleagues in Greater Manchester Police, it would be in the best interests of the family, and for justice, for us to liaise with them," he said. "If he's serious, he needs to make a formal approach. Approaching the media is not formal contact."

Throughout the summer, as the media storm raged around him, with commentators lambasting him for his supposed manipulation of the bereaved families, Brady was lying flat on his back in considerable pain, unable to approach anyone. The mental health tribunal he hoped would be his get-into-jail card (he hates Ashworth mental hospital so much that he would prefer to be in prison) had been cancelled and he was being pilloried in the Channel 4 documentary.

He has only contempt for its makers, condemning the film as infantile and exploitative, "the yellow dog-eared psycho-babble of discredited penal quacks, seeking to build a media career from self-publicity and exploitation of ancient criminal relics ... (It) cynically added to the grief of relatives by deliberate blackmail of witnesses and obfuscation of common facts, long documented, by causing flustered misinformation, re a sealed letter that never existed, to further muddy the waters."

Neither Jackie Powell nor Channel 4 were available for comment. But the programme's accusation of his games-playing clearly rankles with Brady, convinced as he is of the "self-serving hypocrisy ... endemic throughout UK officialdom and the professional middle class".

Whether the games-playing is on his side or that of the authorities, it is clear the culture of mistrust around him and the myth-making that leads to his constant portrayal as a puppet-master may prevent Keith Bennett's body ever being found.

"Knowing the where and when of the past is clearly quite different from stating the where and when of the present," he says. "Given the aforementioned common knowledge of moorland ever-changing heath and bog, and sparsity of static landmarks, what calibre of 'reporter' would believe in the existence of a letter capable of identifying a spot in a yearly changing wilderness which the writer last scanned in 1987?"

Unusually, Brady enclosed a Christmas card in his letter. Although he blamed the Ashworth staff's unreliability for its untimely arrival, he has never sent one this early before, making me wonder if he thinks he may not be here by Christmas. And is this his characteristic tidy-mindedness, trying to tie up loose ends, or is he doing what people say is unthinkable and genuinely wanting to help find the last body on the moor?