I think it was organized crime.
John and Robert Kennedy as AG, both assassinated, both were coming down on the organized crime figures clamping down on the mob, while their father was part of that life as a bootleggger,,, and the Mob has a particularly nasty tradition of dealing with traitors harshly. And covering their tracks.
The KGB would have done it better than Oswald, I agree. The mob would be even better.
Most of the evidence points to Lee Oswald being an informant for the feds (how else do you explain his easy return with Russian wife to the States and his "Fair Play for Cuba" office being located in the same building as the FBI?).
Don't get me wrong - if some arm of our government did get JFK, praise to them. JFK was an enormous danger to the world and getting worse every day. People forget how incredibly dangerous things were back then, how hair-trigger our relations got with the Sovs and how close we came to worldwide extinction. He was infamously fast and loose with the Constitution and the press let him get away with everything. Remember that JFK was responsible for several successful and attempted assassinations (Patrice Lumumba, Dag Hammerschold, Ngo Dinh Diem, and tries at Castro) so in a sense, he died by his own sword.