(NewsNation) — Pablo Fenjves, the ghostwriter behind O.J. Simpson’s book, “If I Did It: Confessions of the Killer,” says Simpson “exploded” when Fenjves told him he believed he was guilty.

“We’d spent a few days together, and he asked me, ‘Do you still think I’m guilty?’ I said, ‘O.J., I’m sorry, I thought you were guilty when I flew down here. And I still think you’re guilty,'” Fenjves said during an appearance Thursday on “Elizabeth Vargas Reports.” “He exploded, he cursed me out. And then he started laughing. … He wanted to put a little scare in me.”

Fenjves was the former NFL player’s neighbor, and he testified as a witness in the 1995 trial that he heard a dog barking the night of the murder.

Twelve years after Simpson was acquitted of double murder, he attempted to cash in on his notoriety and began working with Fenjves.

“I got a call from the publisher, and she asked me to come in and talk about it. … I really didn’t understand what the project meant. It was a hypothetical confession. I said I didn’t want to be in business with O.J.,” Fenjves said.

After receiving documentation that the deal was with Simpson’s children, Fenjves agreed to write the book.

Fenjves said that during his time working with Simpson, there was never “any remorse.”

Simpson died from cancer Wednesday surrounded by his children and grandchildren. In a tweet Feb. 9, Simpson said he had health challenges but indicated he was recovering.

Orenthal James Simpson, also known as “The Juice” on the field, was an award-winning football player who spent 11 seasons in the NFL. However, his athletic success was overshadowed by accusations he killed his ex-wife, Nicole Brown Simpson, and her friend, Ron Goldman.

Simpson was acquitted of the killings in a criminal trial but found liable for them in a civil suit. He later spent time in prison after being charged with armed robbery and kidnapping in Las Vegas.

NewsNation’s Steph Whiteside contributed to this report.