Transcript for What O.J. Simpson said about night of ex-wife's murder in previously unseen interview
Forget everything you think you know about that night because I know the facts better than anyone. Reporter: It's the interview that has sparked a big question. Is this a murder confession on tape? I remember I grabbed the knife -- Reporter: In a bizarre and rambling interview taped in 2006 but never aired until last night O.J. Simpson discusses the 1999 murders of ex-wife Nicole brown and her friend Ron Goldman in stunning detail as if he was there. It was all supposed to be Simpson's hypothetical explanation to promote the release of the book "If I did it." I don't think any two people could be murdered the way they were without everybody being covered in blood. Reporter: There was only ever one suspect in those murders. Simpson himself. He was tried back in 1995 during a captivating 11-month trial that played out on TVs across the country and acquitted. Orenthal James Simpson not guilty of the crime of murder. Reporter: But many have trouble accepting that verdict. Not guilty of the crime of murder. Reporter: Two decades later this newly released interview raising questions once again. It aired as a two-hour special on fox, titled "O.J.: The lost confession." This is very difficult for me to do this. It was very difficult for me because it's hypothetical. This guy Charlie shows up. I don't know why he'd been by a closed house but it told me you wouldn't believe what's going on over there. And I remember thinking whatever's going on over there has got to stop. Reporter: Judith Regan, who interviewed Simpson all those years ago, was actually the publisher of the book. You have the publisher interviewing the person who wrote the book. And that was a great concern to people back in 2006. Reporter: She says she was approached by Simpson's attorney at the time to tell Simpson's side of the story. In the hypothetical I put on a cap and gloves. You reached under the seat for -- A knife. And I remember Charlie saying you ain't bringing that, but I believe he took it. Charlie took the knife? Yeah. In the book. I don't know if Charlie exists. I don't know if it's his alter ego. I don't know if it's him. But that's the name he chose. So Ron Goldman comes in the back gate. Yeah. Nicole had come out. And we started having words about who is this guy, why is he here. As things got heated, I just remember Nicole fell and hurt herself and this guy kind of got into a karate thing. And I said, well, you think you can kick my ass? And I remember I grabbed the knife. I do remember that portion. Taking the knife from dharlie. And to be honest, after that I don't remember except I'm standing there and there's all kind of stuff around. What kind of stuff? Blood and stuff around. He switches from speaking hypothetically, you know, if someone had done this then I imagine they would have done it this way, to "I remember the knife, I do remember that." You write about removing a glove before taking the knife from Charlie. I had no conscious memory of doing that, but obviously I must have because they found the glove there. It was not an easy interview to do. It was very traumatizing for me. And I had just mixed feelings about revisiting the whole thing and what people -- how people would react to it. Reporter: Back then the public never knew the shocking contents of this interview because the backlash was so severe it never aired. The Goldman family and the brown family got upset because they weren't aware of what was actually happening. As a result of the enormous controversy that was ginned up, news corp. Made a decision to cancel both the book and the television interview. Reporter: Judith Regan was later fired. She's none too pleased with fox and the parent company for the way she was treated. Reporter: Then one year later in a twist of fate Simpson arrested again for an unrelated crime. Attempted robbery in that Vegas hotel. He served nine years and was just released last October on parole. According to the executive producer of the fox special, the decision to finally air it was due it's public's overwhelming and continued obsession with the Simpson case. The so-called hypothetical account sparking a frenzy on social media. One person saying yes, this is a confession to murder. Another tweeting, "O.J. Has details and speaks in first person more often than not." But Simpson's lawyer telling ABC news this interview was in no way a confession "But an inflammatory teaser infomercial that would sell books in 2006. There is no way this video would have remained hidden until 2018 if there had been a confession consistent with the actual facts of this case." For Christopher Darden, one of the prosecutors in Simpson's murder trial, watching the interview was difficult. It was painful. I think that people watching this tape are going to be affected. Reporter: Though acquitted of murder, another jury found Simpson civilly liable two years later. He was ordered to pay $33.5 million in damages to the victims' families. O.J. Simpson owes tens of millions of dollars to the goldmans and browns. He still has to pay them with any money he makes outside of his pension. Reporter: In 2007 the Goldman family was awarded rights to Simpson's book by a Florida bankruptcy court, changing the title to "If I did it: Confessions of the killer." Greatly reducing the size of the word "If." Let's immediately go to a picture in Los Angeles. Reporter: Now, nearly 25 years after that televised white bronco chase, America remains captivated by O.J. Simpson. And the Oscar goes to "O.J.: Made in America." Just last year ESPN winning an academy award for "O.J.: Made in America." Ron Goldman, Nicole brown, this is for them and their families. Reporter: If Simpson's story felt like a made for TV movie, it became one in 2016. I'm trying to win. Reporter: With "American crime story: The people versus O.J. Simpson." I'm not black. I'm O.J. Reporter: Tonight the real O.J. Simpson is settling into a life of freedom. And while many are convinced he may have confessed to murder last night, the reality is he can never be tried for those murders again. When you are found not guilty for a particular crime, you cannot be retried for that crime again. It should never be forgotten that two people lost their lives in a really brutal horrible way and there were many victims, including his children who were left behind without a mother. Reporter: For "Nightline" I'm Deborah Roberts in New York.
This transcript has been automatically generated and may not be 100% accurate.