The frightening thing is that all of the usual suspects--CIA, FBI, Mafia--committed assassinations regularly and it would have not been out of character for them. And for most motives, you can't count out LBJ either--whoever wanted Kennedy dead likely had some belief that LBJ would be better for their purposes, and what better way to ensure that than to involve him in the plot?

On the other hand, knowing JFK it could have just as easily been a jealous husband.