The letter doesn't really say anything of value, or anything new.
Everyone who has ever cared has been well aware of both the FBI, CIA, and NYPD's interest in subduing, if not outright murdering, Malcolm X.
Long before this man's "deathbed confession" one of the cops who was undercover and had infiltrated the NOI talked about it. He was the same cop also sent to infiltrate one of the BPP chapters, only to discover the local chapter already had undercover officers infiltrating it.
This is worth a watch.
This doesn't take away the numerous attempts by federal agencies and the NOI on his life - it just illustrates the converging interests between all of those groups.