If you listen to Sammy's rise in the "rampers" it kind of has the same themes. Sammy was #2 behind Papa, they got busted and Sammy claims to have seen a signed statement on the desk of the police sergeant, showing that Papa was cooperating.

Gravano goes back and tells the rest of the gang what he saw, and supposedly [ according to him ] they all turn on Papa, and he becomes the leader. Its all just speculation on my part; was there really a paper on that desk? Was Papa really cooperating?