Brady is believed to have sent the letter to Mrs Johnson via a friend
The mother of Moors murder victim Keith Bennett has spoken of her shock at receiving a letter from her son's killer Ian Brady.
Winnie Johnson, 72, got the two-page letter - dated 21 December 2005 - from the murderer, who is detained at Ashworth hospital near Liverpool.
Brady, 68, complained of his treatment at the high-security hospital.
Keith Bennett, 12, was murdered by Brady and girlfriend Myra Hindley, and is presumed buried on Saddleworth Moor.
Brady's letter repeated his claim that he is being kept alive by force-feeding for "political purposes".
Keith Bennett's body has never been found
Mrs Johnson, in an interview with Sky News, said: "It was a shock to me. He knows a lot more than what he is saying.
"He's admitted he can take police to within 20 yards of where he buried Keith, so that man's not insane, and they just ignored him. Why should they ignore a thing like that?"
Mrs Johnson added: "It's a human life that's gone 41 years ago, and I have had hell since he's been gone."
A spokeswoman for Ashworth Hospital said Brady must have sent the letter to Mrs Johnson via a third party as nobody from the hospital saw it.
Patients' incoming and outgoing letters are inspected visually and opened if there is cause for concern.
Ian Brady was convicted of the murders of five children
"It might have been passed to a visitor to post on his behalf or it might have been via a letter to a lawyer, MP or independent advocate... the hospital doesn't open these letters as these relationships are regarded as a private one," she added.
Despite several police searches Keith's remains have never been found.
Brady and Hindley's other child victims' bodies have been found, but Brady has said he has been unable to find the patch of scrubland where the youngster was buried.
In his letter addressed to "Dear Mrs Bennett", Brady said he was "perfectly rational".
Brady did not refer directly to Keith by name and did not claim he could take investigators directly to the grave but spoke of the "clarity" of his recollections. Brady and Hindley were jailed for life in 1966 for murdering five children.