Clint Hill vowed to never write a book or talk about the 1963 assassination of President John F. Kennedy, but he told 10News, "I am doing it as a tribute. It is historical and should be documented."Hill was with Jackie Kennedy on that fateful day in Dallas, and in his book, "Mrs. Kennedy and Me," he provides details of the shooting that he has kept to himself for decades.For Hill, the memories are haunting and very personal him."I saw the president grab his throat and I knew something was wrong," he said when describing the shooting.Hill threw his body over the back of the presidential car to form a human shield."Mrs. Kennedy had come out of the back of the car and she was trying to retrieve part of the president's head. I put her back in the seat. You could see his eyes were still. There was a hole in his head and his brain was missing," said Hill.The agent codenamed "Dazzle" was just 31 years old. He did everything he could to try to save President Kennedy, but to this day, he said he carries an overwhelming sense of guilt. He blames himself for not reacting a half-second sooner."I had to look into the eyes of the children who lost their father and a wife who lost her husband and I was there and had a responsibility to prevent it and I failed, and it just ate me up," said Hill.Hill said the book has been cathartic for him. He went into seclusion and a deep depression for years.The book reveals the friendship he had with the First Lady and their tragic bond."People don't know how intelligent she was and what an athlete and wonderful wife and mother she was. I knew her. I want people to know who she was, and not what other people thought she was. There are a lot of books out there that just aren't true. This is a tribute, to her," Hill said.Hill will be at a book signing at Warwick's in La Jolla at 7 p.m. on April 14.Hill's book is currently the top-selling nonfiction book in the country.