Scott Peterson breaks his silence on his murder conviction: 'I had no idea it was coming'

Scott Peterson, who was found guilty of murdering his wife and unborn child nearly 15 years ago, is breaking his silence for the first time since the conviction, saying, "I was staggered by it. I had no idea it was coming."

Peterson spoke out from death row in an interview for an upcoming A&E documentary series, "The Murder of Laci Peterson," which premieres Tuesday. The series takes a new look at the case that riveted the nation, after Laci Peterson disappeared on Christmas Eve in 2002 while eight months pregnant. Her and her child's bodies were later found in San Francisco Bay.

John Marks, one of the executive producers of the documentary, said Scott Peterson may have decided to speak out for the first time since his conviction now because he is in the process of appealing his sentence.

"There's an appeals process that's ongoing, so his case is under appeal," Marks told ABC News. "So it felt like a moment, I think, for him and for his lawyer to step up and ... say something about the case."

In the documentary, Peterson described the moment he heard his guilty verdict.

"It was crazy, just this amazing, horrible, physical reaction I had," he said. "I couldn't feel my feet on the floor. I couldn't feel the chair I was sitting in. My vision got a little blurry."

The documentary series revisits most of the key players in the case, including Scott Peterson's former mistress, Amber Frey.

Frey recalls how scared she was when she learned Scott Peterson was a married man with a missing wife and when she had to pretend everything was fine as Scott Peterson continued calling her after Laci Peterson vanished.

In a never-before-broadcast audio recording from 2004, Scott Peterson addresses why he decided to talk to Frey after his wife had gone missing, saying, "The overriding reason throughout it all was she starts giving media interviews, there is no more search for Laci and Conner," referring to the child they planned to name Conner.

"I'd seen what had happened to the search for Chandra Levy with Gary Condit. As soon as it was revealed that he had sex with her, there was no more search for her," Scott Peterson added.

Marks told ABC News that even as the 15th anniversary of the conviction approaches, the new documentary contains details that many never heard before.

"I think when you listen to the witnesses who say they saw Laci in the park, I think that will be really ... that will be kind of a surprise," Marks said.

Marks, who maintained that the documentary is not an exoneration piece, opened up about what he is hoping to accomplish with the series, telling ABC News, "I just want people to say, 'What actually happened here?'"

"The Murder of Lacie Peterson" premieres on the A&E network on Tuesday, Aug. 15, at 10 p.m. ET.