It all comes back to what is seen in the Zapruder film.
Despite many attempts to claim that frames were removed from the film, that images were altered, etc., it's been conclusively shown that the Zapruder film has not been tampered with in any manner.
The Zapruder film shows blood and brain matter exploding from Kennedy's head towards the FRONT, not the rear.
As an aside, I came across one lovely website last night that claimed that the autopsy photos actually prove that Kennedy was struck by no fewer than EIGHT .45 caliber bullets, supposedly fired from at least 3 separate directions.
Face it, folks. Oswald killed Kennedy.
Was he acting alone, on his own volition? No, I don't believe that he was.
But was he the only gunman to actually fire on and hit Kennedy that day?
Yes. I believe that he was.