ITV News understands that police became aware of the possible existence of a letter written by Ian Brady for the mother of one of his victims as early as July 30th.
Police were told about it by Cutting Edge - the television production company that interviewed Brady's mental health advocate Jackie Powell for a documentary that will air on Channel 4 on Monday. Cutting Edge conducted the interview with Jackie Powell on July 20th.
Greater Manchester Police had discussions with Jackie Powell prior to arresting her and searching her home.
We understand they have removed a number of documents from her house and are examining them, but have not yet found any information that might bring them closer to finding the whereabouts of Keith Bennett's body.
We understand Ms Powell herself has told police that she no longer has the letter and it may not even exist any more.
A search of Brady's cell has also revealed nothing.
This morning, Ms Powell told Sky News that her words in the documentary have been "misrepresented" and "blown out of all proportion".
For more on this story, visit the ITV national news site.