Jackie — and Ari.
As I understand bullet ballistics, entry wounds are smaller than exit wounds. Given that, what I can’t square in the Donahue theory is the final, mortal wound: going by the Zapruder film, it appears that the bullet entered the front of the head because bone and tissue fly backward, away from the front. If that wound is supposed to have hit the back of the head first, I would expect that material to be flying forward.
The theory also begs another question: was every round from that Secret Service agent’s weapon accounted for when it was returned to the armory?