Oswald was JFK's killer, but there may have been others who knew what he was up to before he actually pulled the trigger. If his wife, Marina was aware of what he was going to do, I can see why she would not have wanted investigators to know that. He may have shared his plans with others too, but how can we ever find out if he did? It was an easy shot from the window that he used as a perch. I've been there and I have shot crows in flight with a rifle from a greater distance than that, even without a scope. It is a coincidence that he happened to work in a place where the motorcade was going to pass, but history is full of stories like that. If Oswald had worked at a warehouse on the outskirts of Dallas, we might not have ever heard of him. JFK was a convenient target of opportunity for a murderous crazy who was trained to shoot by the US Marine Corps, that's probably all there is to it.