Jackie shot JFK in the head, literally blowing his brains out so part of his brain is seen hanging out the right side of his head when he falls over. He is instantly dead.
Jackie's right hand held the murder weapon and when you see her hand go up, that is her getting rid of the weapon immediately after the assassination. The weapon goes onto the trunk.
She climbs back onto the trunk to retrieve it but Clint Hill Beats her to it. He retrieves the weapon from the left rear of the trunk where it had fallen and gives it back to Jackie.
Watch the white dot in the background that appears to be something in the grass outside the limo but is actually drawn in, frame by frame from the moment of the head shot. Watch the way the white dot jags unnaturally. At the point that Jackie raises her hand, it is no coincidence that the white dot is in precisely the right position to conceal what was in her hand. The white dot was drawn in to conceal the murder weapon and frames were removed from the film to conceal the murder weapon as it left her hand. All of this was very intentional to hide that Jackie was the assassin!
Everyone in the Limo except for JFK knew about the assassination and participated in it.