John F. Kennedy Jr. Biographers on What Happened During the Night of His Tragic Plane Crash (Exclusive)

More details about John F. Kennedy Jr. 'sdeath are coming to light.

In an interview with ET's Rachel Smith, biographers RoseMarie Terenzio and Liz McNeil revisited the tragic day Kennedy, his wife, Carolyn Bessette, and sister-in-law, Lauren Bessette, were killed when the plane he was piloting crashed.

Prior to the crash, Terenzio, Kennedy's former assistant, recalled how John F. Kennedy andJacqueline Kennedy's son viewed flying as "his escape."

"It was the one place where he could be alone and no one was wondering what he was doing, and watching where he was going, taking his photograph and wanting something from him," she told ET. "He was just up there alone. [There was a]freedom and I think a sense of peace. I think it gave him a lot of peace."

That changed on July 16, 1999, when his plane went down into the Atlantic Ocean off Martha's Vineyard, Massachusetts.

"We spoke to one of the investigators at the NTSB -- National Transportation Safety Board -- who was part of the investigation, and there are multiple factors about what happened that night," McNeil, a journalist, told ET. "There's the late hour. They were late getting to the airport and there was horrendous traffic that night. There was also deep haze, a very thick haze, it makes visibility very difficult."

"John [was] not instrument-trained. He was legally able to take off in those conditions, but what I think happened was the weather had changed. There were about two hours between leaving the office and getting to the airport," she continued. "When he turned off over to basically begin descend into Martha's Vineyard, it's completely black. As the investigator said, John was looking for visual cues and there were no visual cues."

That night, and Kennedy's life leading up to it, are all discussed in Terenzio and McNeil's new book, JFK Jr.: An Intimate Oral Biography . Kennedy's death was preceded by other tragedies, first of which was his father's 1963 assassination, when he was a toddler.

"I think one of the things that surprised me was how much his father's death affected him, even though he never talked about it,"Terenzio told ET of what she learned while conducting research for the book."He never talked about his father much and he never talked about his father's death. I think that in the process of interviewing all these people [I learned that] he was just seeking and searching for that connection all the time."

Then came Kennedy's mother's death in 1994 after a battle with cancer.

"A lot of the stories in the book from his close friends talk about how much her death impacted him, and how close they were, and what that meant in his life," Terenzio said. "It kind of forced him to grow up. Not that he wasn't an adult, but I think... [there] was part of him [that was] really coming into his own and becoming fiercely independent."

The same year his mother died, Kennedy began dating his eventual wife.

"I think Carolyn was, in some ways, a lot like him. They were both very accessible. They were down to earth. They were real. They each had their group of real friends that they had for a long time," Terenzio said. "Carolyn wasn't famous when she met John. She was a girl about town in New York City, working a dream job [at Calvin Klein] and hanging out with models and celebrities, but she wasn't famous."

"I think that was one of the things that attracted John to her. I think he liked the fact that she was this kind of working New York City girl who had a life of her own," she continued. "He loved the fact that she was fiercely independent... In addition to the romance, it bonded them in a friendship."

Their love went both ways, withMcNeil telling ET, "Another thing with Carolyn that a lot of people told us was how protective she was of John. She was watching out for things like people taking advantage of him. [She was] sort of an eyes and ears for him."

As they worked on their book, the women interviewed everyone from a secret service agent to Kennedy's favorite waitress, from former president Bill Clinton to Mike Tyson, from his childhood friends to Brooke Shields.

"He connected with so many different types of people," Terenzio said. "He kept a lot of his friendships from grade school throughout his life."

Putting the book out on the 25th anniversary of Kennedy's death,Terenzio said, felt like the perfect way to remember the attorney and magazine publisher.

"What we found with the book and the people that we were interviewing was that enough time had passed that people wanted him to be remembered and they thought it was an opportunity, on the 25th anniversary, to really kind of bring him to life again," Terenzio said. "Enough time that had passed that it felt like celebrating him, rather than mourning him."

"I think John understood in a profound way that he had an emotional connection to this country and to people around the world," she added. "I think if he knew he were gonna be gone at 38, he wouldn't [want to have been] forgotten."

JFK Jr.: An Intimate Oral Biography is due out July 16, the 25th anniversary of the late attorney's plane crash.

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