The secret service agent employed to protect Jackie Kennedy has recounted the terrifying moments after the president's assassination in 1963, and how the First Lady scrambled to reach his limp body.
In a memoir, Clint Hill, now 80, reveals his sheer determination to throw himself between the Kennedys and the bullets as parts of the president's brain and skull splattered over his shirt.
As he moved towards Mrs Kennedy, he watched her reaction: 'Her eyes were filled with terror,' he wrote. 'She was reaching for something. She was reaching for a piece of the President's head.'
Hill was alongside the presidential vehicle when John F. Kennedy was shot in the neck and head before he slumped into his wife's arms while driving through Dallas, Texas in November 1963.
Hill is the figure in the famous Zapruder film of the shooting which shows him climbing onto the back of the president's limousine.
In his book Mrs Kennedy and Me, Hill recalled the crowds cheering for the motorcade and the moment he heard an explosion. He looked around and saw the president grab his throat.
'Somebody had fired a shot at the President, and I had to get myself between the shooter and the President and Mrs. Kennedy,' he wrote. 'Nothing else mattered.'
Before he could reach them, two more bullets were shot - the final one hitting the president in the head, just above his right ear.
'The impact was like the sound of a melon shattering onto cement,' he remembered, adding that the President's blood and parts of his skull splattered over his clothes, face and hair.
Pulling Mrs Kennedy, as he always called her, into her seat, the president's body fell into her arms with his eyes open. 'Jack, Jack, what have they done to you?' she wailed.
Hill, who has previously said he could have taken the third bullet had he moved a second sooner, then had the thought: 'How did I let this happen to her?'
Speaking to People magazine, which published excerpts of the book, Hill added: 'Because of the angles, the weather, where we were - everything - I did all I could. But I still feel guilt.'
He then goes on to describe the scene at Parkland Hospital, where he waited outside the trauma room with Mrs Kennedy. He describes how 'the light was gone' from her eyes.
While there, Hill took a call from the president's brother, Robert Kennedy, who was demanding to know how bad the situation was.
Haunted by the image of the president's head being hit by the final bullet, but uncertain how to tell Robert that his brother had been killed, Hill said simply: 'It's as bad as it gets.'
As a doctor approached the group, they knew it was terrible news and Mrs Kennedy ran to be at her husband's side. An agent approached Hill and told him the president had died.
Later, the book recounts, Hill accompanied Mrs Kennedy and Robert Kennedy to see the body.
Hill remembers how, once there, Mrs Kennedy lovingly cut her husband's hair with scissors that her secret service agent had brought, leaving chestnut locks on the blades when she gave them back.
Hill continued to work as Jackie Kennedy's agent for a further year after the death. During his time working with the family, he had grown close to the former first lady, which he admits was unusual.
He recalled stories of sneaking cigarettes together in the back of the car during drives, and offering her advice ahead of the trip to Dallas after she expressed fears about their safety.
But despite what has been claimed in the past, he did not love her. 'I admired her,' he told People magazine. 'We grew closer and closer [but] I don't think you can say I was in love with her.'
A year after the assassination, he went to work for Lyndon Johnson. But he quit in 1975 after guilt he felt from the shooting made him turn towards alcohol.
Although he kept in touch with Jackie Kennedy for a few years after he stopped working for her, when he heard about her struggle with cancer in 1994, he could not bring himself to lift the phone.
'I knew that the mere sound of my voice would take her back to that day that changed everything,' he wrote. 'And the sound of her voice would do the same to me.'
Lee Harvey Oswald was accused of firing the three shots that killed John F. Kennedy. As he was being transferred to jail, he was shot in the stomach by a man, Jack Ruby, in the crowd.
He died in the hospital where Kennedy had passed away 48 hours earlier.