They were eight seconds that changed the world - former marine Lee Harvey Oswald leaned out of the sixth-floor window and squeezed the trigger on his bolt-action rifle three times.
As a bullet blasted through John F Kennedy's neck, hero secret service agent Clint Hill was the first to react, leaping out of a following car and racing towards the presidential limousine.
Without a thought for his own safety, Clint leaped on to the back of the accelerating car, trying to create a human shield to protect the president and his wife Jackie.
But he was seconds too late. Before Clint could scramble into position, another shot pierced President Kennedy’s head, shattering his skull and showering blood and brain matter all over the car.
In an exclusive interview with Sun Online on the 55th anniversary of the assassination today, Clint, 86, reveals how he will never be able to forget the shocking and gruesome image of the president's last moments.
And, tragically, even now Clint still believes “he should have been faster” - and blames himself for the president’s death.
“One thing that I've never been able to erase from my mind is being on the back of the car looking down at the president, who was lying with his face in Mrs Kennedy's lap," he said.
“The right side of his face is up and I can see that his eyes are fixed. There's blood everywhere.
"I can see the gunshot wound. In the room that's in the skull I can see that there is no more brain matter left.
“That is something I could never, and have never been able to, erase from my mind.”
This article originally appeared in The Sun. For more from The Sun, click here.