And BTW, the CIA has recently declassified some memos dating back to the 1960s, including those relating to the Cuban Missile Crisis, and even those memos already make clear that the Cubans and Soviets were the most likely people to have Oswald assassinate him.
Among the things revealed is that Oswald, on September 28 1964, met with both the Cuban and Soviet embassies to get a path back to the latter to escape the USA. Now ask yourself this, why specifically choose the Cubans and the Soviets as the escape route if he was merely doing a hit for Mafia or even the CIA? Also, Johnson got that report three days after the shootings, meaning he was not likely to have been involved in the hit at all.
Our deepest cover spy, Morris Childs, was in Moscow with the Soviet leadership when JFK was shot. They were riveted to the news and were coming up with all sorts of theories about who could have done it. No one broached the idea that this could possibly be one of their own. And in a rigidly top down system it would be unthinkable.
The Soviets were our great enemy. But they had a grudging respect for American leaders, including for Kennedy. Assassination wasn’t their style. For Castro, that’s a whole different matter and it’s something he would do.