"The ultimate question is, did Michael Jackson ever molest a child?" he said. "My conclusion is that I don't think he did. I wish I could say conclusively, 'no he didn't.' I can't. There is a shadow of doubt. And I had to come to accept I was going to have to live with it. And I think anyone who is honest about Michael will have to learn to live with it too.
"He wanted to be a child himself," he continued. "He wanted to believe that he was another 12-year-old or 13-year-old... He wanted a sleepover. He felt he didn't get childhood."
Jackson was a star from a young age, perhaps too soon. He became the focal point of the family at age 7 as the lead vocalist on many Jackson Five smash hits, including "I Want You Back," "ABC" and "I'll Be There."
"People want to believe that the Jacksons are a family of very, very talented people," Sullivan said. "Really there was one very, very talented person. I mean Jermaine has a bit of a voice, but I don't think he'd have risen above the level of lounge singer without Michael."
Michael, desperately lonely, apparently sought the company of a handful of other people who could understand his level of fame. He was, Sullivan said, given the brush-off by Jackie Kennedy Onassis and Princess Diana.
"For lack of a better word, I think [Diana] was a little creeped out by him because of the intensity of his desire to be with her," Sullivan said.
Sullivan said he tried and failed to interview family members for his book, including Joe Jackson, but claims the patriarch has mellowed with age.
"He's a comical figure in a lot of ways," he said. "People would tell me he was carrying a gun in the waistband of his pants a lot and would always let them see to let them know that at 84 he's still a bad dude, or he would make a point of telling people, 'When I go to visit Katherine, she stills cuts my toe nails.' Like, 'I'm the man.'"
In the book, Sullivan describes how various people, including Michael Jackson's wife Lisa Marie Presley, were beguiled by the star's intelligence and charm. Sullivan himself admitted that he too felt a "deep affection" for Jackson after writing his book.
"I hope I fell for what's good about him," he said. "I don't think I ever was blinded to the aspects of Michael's character that are not so attractive, or questionable."
In all, Sullivan's book sprawls over nearly 800 pages, including 165 pages of bibliography and notes.
"You're relying on sources and in Michael Jackson's universe you have to bear in mind, there is no one with truly clean hands," Sullivan said. "So you're talking to people that always someone, some people have accused of this or that or who has this is or that issue. That was Michael Jackson's world."