the New York Times is carrying this article from Clint Hill, who was the Secret Service agent who leapt on to the back of the Kennedy’s limousine after the President was shot.
We were traveling through Dallas en route to the Trade Mart, where the president was to give a lunchtime speech, when I heard an explosive noise from my right rear. As I turned toward the sound, I scanned the presidential limousine and saw the president grab at his throat and lurch to the left.
I jumped off the running board and ran toward his car. I was so focused on getting to the president and Mrs. Kennedy to provide them cover that I didn’t hear the second shot.
I was just feet away when I heard and felt the effects of a third shot. It hit the president in the upper right rear of his head, and blood was everywhere. Once in the back seat, I threw myself on top of the president and first lady so that if another shot came, it would hit me instead.
The detail went into action. We didn’t stop to think about what happened; our every move and thought went into rushing the president and Mrs. Kennedy to the nearest hospital.
you can read the whole thing here.