Giancana definitely sticks out in that category. Shot in the back of the head while in his own home by someone he was comfortable enough with to invite inside and cook sausage+peppers for. It had to be someone close to him. No doubt about it.

Also with Chicago I would throw the Anthony Zizzo murder/disappearance in there. In the life for 50+ years then vanishes after an alleged beef with Michael Sarno whom he supervised so that would also implicate the rest of the outfit or at least hierarchy. I know it's just a theory and most likely will never be solved but I don't believe for a minute that he just went on the lam.