This is an exclusive interview with peter roger, the father of Elliot roger, the young man who killed 13 near Santa Barbara last month. And ever since the start, people have wondered, were there... See More
This is an exclusive interview with peter roger, the father of Elliot roger, the young man who killed 13 near Santa Barbara last month. And ever since the start, people have wondered, were there warning signs the parents should have seen. Peter roger, the father, sitting down with ABC's Barbara Walters. How are you? Every night, I go to sleep. I wake up and I think of those young men and young women that have died. And were injured and were terrorized. And my son did that. My son caused so much pain and suffering for so many families. When you wake up in the morning, what do you think? It's like a reverse nightmare situation. When you go to sleep normally, you have a nightmare and wake up and everything's okay. Now, I go to sleep, I might have a nice dream. And I wake up, and it's slowly the truth of what happened dawns on me. And that's my son was a mass murderer. You did not think that Elliot was suicidal, or certainly not homicidal. There's no way I thought that this boy could hurt a flea. I mean, this is the most unbelievable thing, Barbara, and what I don't get. We didn't see this coming at all. Awesome to imagine being a parent of a child. Can't imagine that. You can watch Barbara's interview, tomorrow night, "20/20," 10:00, 9:00 central. Let's go back to ginger and
This transcript has been automatically generated and may not be 100% accurate.