In his first interview, Peter Rodger told ABC News' Barbara Walters that he was shocked to learn that his son, Elliot, had killed six people and wounded 13 others in Isla Vista., Calif last month. "We didn't see this coming at all," Rodger said, adding that prior to the rampage he didn't think his son "could hurt a flea."

Since the shooting, Rodger said his life has been like a "reverse nightmare."

"When you go to sleep normally, you have a nightmare and you wake up and, 'Oh, everything's OK,'" he said. "Now I go to sleep, I might have a nice dream. And then I wake up and it's, slowly, the truth of what happened dawns on me. And you know, that is that my son was a mass murderer."

"Every night I go to sleep, I wake up and I think of those young men and young women that have died and are injured and were terrorized when my son did that. My son caused so much pain and suffering for so many families."

In a statement with Peter's mother released last month, Rodger described the situation since the shooting as "hell on earth." The full interview with Rodger will air on 20/20 on ABC Friday night.

[via ABC News]