It could only mean the Soviets were behind it and kept secret to avoid a war.
The CIA. Why wouldn’t you not want them exposed if they did it?
MK ultra Brennan and Dulles
This is a plausible theory. I'm sure the Soviets were very angry about being humiliated during the Cuban Missile crises. Given their mindset, it doesn't surprise me that they would want Kennedy killed, and Oswald was just the sort of pro-soviet idiot who would do it.