Somehow the article never finds it appropriate to point out that Kennedy was killed by a commie, not a right wing extremist.
That's one theory.
A second holds that Kennedy was out to get Castro and Fuzzy Face bumped Jack off first.
A third holds that Papa Joe and Jack double-crossed the Mob -- who stole the Rat nomination fair and square for Jack by delivering the unionized West Virginia coal miners in the primary (finally putting Jack over the top) -- and then stole the general election fair and square by delivering Chicago (and Illinois) along with mayor Daley in the general election -- only to be betrayed by attorney general brother Boobie who went after the boys in the pinstripe suits with a vengeance. The Mafia in turn did to Jack what they do to everyone who everyone they consider to be a traitor.
Any way you slice it, your main premise holds. Kennedy was bumped off by someone other than a right wing nut.