IN LATE APRIL, 2006, Judith Regan, the publisher, called me about a highly confidential project. O.J. Simpson was going to write a book for her, she said, to confess to the murders of Nicole Brown Simpson and Ron Goldman. Only it wasn’t exactly a confession. The book was going to be called “If I Did It” and it would be sold as an account of what might have happened on the night of the murders. When I told Judith I wasn’t sure I understood what that meant, she said, “He wants to confess, and I’m being assured it’s a confession. But this is the only way he’ll do it.”

As soon as we got off the phone, I spoke to the only two other people at ReganBooks who were in the loop. One was a senior editor, the other a company attorney. I already had misgivings about the book, partly because I didn’t understand what O.J. was selling, and partly because there are laws about criminals cashing in on their crimes. I knew that this law only applied to convicted criminals, but that didn’t make it any easier to swallow.

No, no, no, I was told. O.J. himself wouldn’t be making a penny. All the profits were being funneled into a corporation that was owned and controlled by his children. I thought that sounded more than slightly suspect, but I’m not an attorney. Surely, if a deal was being made with O.J.’s kids, it was being done with the blessing of the parent company, News Corp., and the powers that be at HarperCollins.

Of course, part of me didn’t want to probe too deeply. I was being given an opportunity to sit in a room with O.J. Simpson and listen to his confession, or an ersatz version of a confession, and it was simply too good to pass up. That he wanted to describe it as “hypothetical” meant very little to me. I’d assumed from the start that he was guilty, and in the years since I’d heard nothing to make me change my mind.

Not long after, I had lunch with the attorney who had brought the project to Judith. He told me that the idea for the book, and the bizarre title, had originated with a guy who operated on the fringes of the entertainment industry, and who was friendly with O.J.’s eldest daughter, Arnelle. I still wasn’t entirely sure what, exactly, the book was supposed to be, and neither was he, but I was assured, as Judith had been, that O.J. would be confessing, and that I’d be hearing details only he could possibly know. By the time the check arrived, we had hammered out a deal. I would be paid a guaranteed, upfront fee, plus a share of the book’s profits.

I kept waiting for the attorney to ask me about my history with O.J., but he never did. Ten years earlier, during the criminal trial, I testified for the prosecution. I had described the “plaintive wail” of Nicole’s dog, and Marcia Clark used the information to try to establish a timeline for the murders. I lived on Gretna Green Way, one street over from Bundy, and I shared a back alley with Nicole. On the night in question, the unhappy dog had begun to make himself heard at around 10:15 or 10:20, leading to the assumption that the murders had already taken place. If that was indeed the case, O.J. would have had plenty of time to get home, wash up, and climb into the waiting limo for the ride to the airport.

I flew down to Miami in early June, and the following morning I went off to meet O.J. at a Coconut Grove hotel. The attorney was waiting for me in the lobby, along with one of O.J.’s handlers, and we went up to the suite they’d booked for the occasion. We waited. And we waited some more. O.J., apparently feeling skittish, didn’t show up until noon. Even then, reluctant to come upstairs, he rang from the lobby and asked if we might meet in the hotel restaurant.

He was already seated when we arrived, and he stood to greet me as I approached. He had a hard time getting to his feet—he had a bum knee—and looked like an older, faded version of his former self, heavier, with an unhealthy pallor, his hair going gray. He thanked me for making the trip, apologized for being late, and offered me his hand. It felt as big as a baseball mitt. He then gestured toward the empty chair beside him, and before I’d even settled in he said, “Tell me something. What is this ‘wailing dog’ bullshit? You ever hear of anyone putting a man away based on the testimony of a wailing dog?”

Okay. I got the message. He remembered me from the trial, and he wanted me to know he remembered. Or maybe he didn’t remember, but someone in his camp had the sense to Google me before I flew down.

We had lunch, and he talked a little bit about his knee, and about his arthritis. I wondered if he was trying to elicit sympathy, but I was thinking about something else entirely. I kept asking myself why he had agreed to write this crazy book, and I could only come up with three reasons: One, he needed the money. Two, he missed the attention. And three, he genuinely wanted to confess. I was hoping for number three, of course, but there was one other nagging possibility: The whole thing was a con.

After lunch, we made our way down the corridor, with O.J. limping beside me, the attorney and handler close behind. We got into the elevator and went up to the suite, and I readied my laptop and recorder. I generally don’t tape my interviews—I type pretty fast, and the typing itself somehow brings everything into sharper focus for me: words, tone, attitude, voice. In this case, however, I thought taping was a good idea.

O.J. dropped into a chair, grimacing, and plunged right in: “I’m not going to talk about the murders because I wasn’t there that night and I don’t know anything about it.”

“Excuse me?”

“You heard me.”

I turned to look at the attorney. “Then why am I here?” I said. “It was my understanding that I was going to hear a confession, or at least a hypothetical confession.”

“I’m not confessing to anything,” O.J. said. “I have nothing to confess.”

I excused myself to call Judith in New York. I told her what was happening and suggested we pull out, but the attorney asked if he might have a word with her. I handed him my cell phone and left the room, rejoining O.J. He gave me a look and shook his head. “I always thought this was going to be fiction,” he said.

“Fiction? I don’t know where you got that idea. This isn’t fiction. I only write non-fiction books. I save the fiction for my screenplays.”

The attorney reappeared and told O.J. they should take a little walk. They returned two hours later with O.J. back on board.

He had misunderstood—it was as simple as that. But he didn’t want to talk about the murders until later, so he wondered if we might start with the “easy stuff.” That had been my intention all along, so the attorney left us alone and we plunged in. We began with the day O.J. met Nicole. We talked about his crumbling marriage to Marguerite, his first wife. We talked about his childhood and about his late father, with whom he had a falling out that lasted for the better part of a decade.

He was smiling by the end of the afternoon. It hadn’t been that tough, he said. He liked it. Yeah, I told him. Ghostwriters are unlicensed therapists. “Don’t be afraid to cry,” I said, only half joking. “Everybody cries.”

“I’m not crying for you, motherfucker!” he said, but he was laughing.

The next day was a little tougher. He told me that he had only struck Nicole once in all the years they were together, once, and the press had turned him into the poster-boy for wife abuse. And none of the problems were his fault. It was all her. Everything.

The term “malignant narcissism” popped into my head.

By the end of the day, we had made it all the way to the night of Sydney’s recital, the night of the murders. Sydney had looked adorable on stage, he said, but Nicole was dressed like a teenager. “What did she see when she looked at herself in the mirror?” he wondered.

After the recital, Nicole and the family went to Mezzaluna for dinner, and the press made a big deal about the fact that O.J. hadn’t been invited. That was bullshit, he said. He had an open invitation. He just hadn’t wanted to go. Instead he went home, called his on-again off-again girlfriend, Paula Barbieri, didn’t reach her, and found himself going for a burger with Kato Kaelin, the houseguest.

At that point, O.J. was beginning to look a little uneasy, though it’s possible he was just tired, so we called it a day. I walked him down the corridor and we got into the elevator. There was a guy inside on his cell phone, and his eyes went wide with surprise. “Holy shit!” he said. “I’m in an elevator with O.J. Simpson. I’ll have to call you back.” He reached for O.J.’s hand, grinning ear to ear, and O.J. took it. When we got to the lobby, there was more of the same. People turned to stare, but there was no horror in their looks, no disgust, no judgment. A young couple came over and asked O.J. if he’d pose for a picture, then handed me a camera and had me do the honors. It wasn’t the only time this happened. The next morning, O.J. didn’t show. I called his handler, who couldn’t find him. He called several hours later to say he’d finally managed to track him down. O.J. was a little nervous about the day ahead, he explained, because he knew we were going to be talking about the night of the murders. “But don’t worry,” he said. “He’ll be there.”

O.J. showed up two hours later and had trouble focusing. He was restless and angry. At one point, he said, “You know what kills me? All the goddamn people who assumed I was guilty before they’d even heard my side.” He looked...