Don't look for a zebra in a field of horses. Someone just tried to assassinate Michael. Michael knows this wasnt amateur night and whomever planned this sent the culprits on a suicide mission, just like he does with Rocco. If Rocco was in on killing Michael, Michael would have to eliminate Rocco as quick or quicker as they did with Paulie. Rocco was more powerful and closer to Michael than Fredo and Carlo. If Michael thought it was Rocco, he knew he wouldnt get a second chance. I remember the post about the Rosatos killing Clemenza by poison or something. Come on now.