Earlier quoted context omitted.
There is a chance there wasn’t anything incriminating. The top guys kept conversations live or intimated they wanted something done; the lowers took the planning and execution upon themselves.
Mobsters have it down to an art. "You take care of it." means "Murder him and dump the body into a building foundation." "I don't see any problems." can mean "The ambush will happen at the scheduled time. Vinnie will clean up the bodies." etc. You'll also see a lot of politicians using "dog whistle" statements, that are interpreted by listeners to mean something entirely different from the stated words.
Non-mobsters aren’t always as careful. There is a good chance these guys just weren’t properly investigated.