LOS ANGELES - The father of a 22-year-old man who killed six college students and himself near Santa Barbara, California, says he had long known his son was deeply troubled but realized too late "the monster" lurking within him.

Peter Rodger, an assistant director on the film "Hunger Games," told ABC's Barbara Walters in an interview televised on Friday that he initially thought his son, Elliot, was one of the victims, rather than the killer, in the May 23 massacre.

Rodger recounted first learning something terrible was afoot while dining with friends that night about 100 miles (161 km) away in Los Angeles and receiving an email from his son with a lengthy, menacing manifesto titled "My Twisted World".

Moments later, Rodger received a phone call from his ex-wife, Elliot's mother Li Chin, who had gotten the same email and then googled their son's name to find a chilling video he had posted on YouTube called "Elliot Rodger's Retribution."

At that point, the father recalled, "A really dark force of horrible energy hit me." He hastily embarked on a desperate road trip, hoping to reach his son in time.

"We were just driving up there in absolute fear for him and confusion," Peter Rodger said.

Elliot Rodger had by then already begun his killing spree, stabbing three people to death, including his two roommates, at their beachside apartment in the town of Isla Vista.

As Peter Rodger neared his son's home, local news media had begun reporting that a gunman was on the loose. In the end, three more college students were shot to death and 13 other people were wounded before Elliot committed suicide.

Peter Rodger said he was devastated by news that his son was among the dead but did not learn he was suspected of being the killer until seeing it reported hours later on the Internet.

Rodger insisted he never imagined his son capable of violence, despite chronic social problems Elliott had suffered among his peers since boyhood and years he had spent in therapy.

He was aware that his son was obsessed with having never had sex, and once suggested taking him to Las Vegas to lose his virginity, an idea his son rejected.

Rodger recalled rebuking his son years later when he found out he had been dabbling in websites devoted to misogynist ideology, but even then did not appreciate the level of hatred his son harbored toward women.

Rodger said his son was "incredibly brilliant at hiding" his inner demons and expressed remorse for the pain that has caused the victims' families.

"I wish that these families didn't have to go through this terrible ordeal," Rodger said. "It's very hard for them to understand that I didn't know the monster that was in my son."