I like the theory that was mentioned in the movie "Drillbit Taylor."
Castro did it, because he was jealous that he couldn't "score" with
Marylin Monroe, and JFK could. So he did it.
And speaking of Bobby, they profiled it on Unsolved Mysteries once, and
it was someone who claimed to have taken photos of the entire event,
was arrested by detectives and they destroyed his photos of the
shooting. The photographer was a high school student at the time.
They only kept his first roll of film, and parts of the second and
third rolls. They documented it as one roll of film. They don't know if
this person actually saw the shooting, even though his story was very detailed, because some of these details sound like "coincidences" such as standing on a table on the opposite side of JFK where he was shot. They found photos of someone standing on a table as he described, and ruled it as one of those "coincidences". Given the fact that detectives
stopped him, took him in for questioning and destroyed some of the
photos makes it sound suspicious.