The lawyer for Winnie Johnson, John Ainley, has said he is not "holding his breath" that recent developments will lead to the location of her son's body.
He told Sky News: "It may be at this late stage that he [Ian Brady] has got some sort of conscience about all of this" but he said that he would be surprised.
Mr Ainley added that Ms Johnson's family is "reassured that the police are investigating" but that he did not think its was advisable to raise her expectations.
Police first became aware of the possible existence of a letter from Ian Brady to his victim's mother in late July.
An advocate for Moors murderer Ian Brady has revealed the possible existence of a letter that may reveal where one of his victims is buried.