I was always told that it was a sort of mafia tradition that you pick out a guy who is a "likely suspect" and get him lined up to actually do the hit, and then, most of the time, no one will really look around for anyone else. There were, I'm almost sure, many, many other people who were in on this.
As for hating the Kennedys: they were creeps. I don't know what people are so impressed with. You solicit help from mobsters to get you elected. They help you. You and your brother then turn on them. You're filthy rich. It is easy to do great things when you are filthy rich, but not so easy to do great things when you have nothing but the clothes on your back, a killer instinct, and a will to move your family up in the world. I would give my bootlegging, bank robbing, money laundering uncles and grandfathers the title of hero before I ever gave it to JFK... but that may be just me.