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(CNN) - There are so many iconic images from that horrific period that began 50 years ago with the crack of an assassin's rifle: John Kennedy Jr.'s salute at his father's casket, Lyndon B. Johnson being sworn in on Air Force One next to Mrs. Jaqcueline Kennedy, still wearing her blood-stained suit.
And then of course – the image of the suddenly tragically widowed Jackie Kennedy and a Secret Service agent scrambling to protect her.
Earlier this week CNN's Jake Tapper had the rare honor of moderating a panel at the Newseum with that agent, Clint Hill, the man who that day ran towards the target.
"I got on the back of the car," said Hill. "I grabbed a hold of the handhold, had my foot up on the rear bumper platform, and the driver hit the gas. When he did that, I came off, I slipped, and I had to run two or three more steps before I could get back up there."
"In that time frame, Mrs. Kennedy came up on the trunk. She was trying to grab some of that material that came out of the president's head. She was trying to pull it back. She didn't even realize I was there," said Hill, who eventually grabbed Mrs. Kennedy and pulled her into the back seat.
"When I did that, the president's body fell farther to the left, with his head in her lap, and the right side of his face was up, and I could see his eyes were fixed. I could see through that hole in his skull, most of that brain matter was gone in that area. So I assumed it was a fatal wound," said Hill.
Hill then turned around, and gave a thumbs down to the other agents, signalling the seriousness of the wound.
"I had this sense that we had a responsibility to protect the president that day and we failed. There isn't any question about that because he’s dead," said Hill.
"I felt a sense of guilt, because of all the agents working that day I was the only one who had a chance of doing anything. The way everything developed, the way all the other agents were positioned, I was the only one who had a chance to either get to the car or to do anything, and I couldn't get there fast enough.
The guilt ate at Hill, driving him to isolation and substance abuse.
"I finally, just, pretty much lived in my basement with a big bottle of scotch and a bunch of cigarettes for about six years," said Hill. A doctor snapped him out of it.
"By 1990 I went back to Dallas. I walked the streets of Dealey Plaza, Houston street, went up in the Texas School Book Depository, went up to the 6th floor, looked out that window. I checked all the angles, the weather, everything I could think of," said Hill.
"I finally came to the realization, he had all the advantages that day, we didn't have any. And I did everything that I could, there was nothing more that I could have did," said Hill.