Just McCane, as far as Gaspipe's contacts are concerned. Casso was one of the few mobsters to supply info for a pseudo autobiography. That's the only reason the general public is aware of his FBI leak.

I gotta figure other dons had agents in their pocket, but they didn't write books. It's been said that Hoover stayed away from the mob because he didn't trust that he could keep his agents from being corrupted. I don't believe this was just a hunch on Hoover's part- he probably had intel that supported his fears.

Didn't Whitey Bulger have his own FBI guy in his pocket?