In May, Rodger's three roommates were fatally stabbed in an apartment building while three more were shot to death near the campus of UC Santa Barbara. Rodger was later found dead from what is believed to be a suicide.
"What is so significant about Barbara Walters getting Peter Rodger is that we don't see the parent of a shooter going on-air and telling their side of the story," said The Hollywood Reporter's Michael O'Connell. "Especially so quickly after what happened."
ABC will air Peter's interview at 10 p.m. on Friday during a special edition of 20/20.
"It's like it was a reverse nightmare situation," Peter told Barbara. "I go to sleep and I might have a nice dream, and then I wake up and slowly the truth of what happened dawns on me and that is that my son was a mass murderer."