The Dictaphone evidence was thoroughly discussed (and debunked) in Gerald Posner's "Case Closed."
Uh..., read Posner's book; didn't think much of it.
The thing that's always struck me about the Kennedy assassination is how bass-ackwards the Warren Commission was in its investigation. In any murder, the authorities look at the facts and allow the facts to lead to the truth. But the Warren Commission seemed to start with a premise (Oswald- single lone assassin) and tailored the facts to fit their preconceived notion.