Transcript for Elliot Rodger Plans for the 'Day of Retribution'
We return to the secret life of Elliot Rodger. Once more, Barbara Walters. Reporter: For Elliot Rodger, Santa Barbara was the picture perfect version of his ideal life. There were hot blonde girls walking around everywhere. If I can't get laid there, then there is no hope for me at all. Reporter: At 19, Elliot was stuck in a cycle of isolation and depression. His parents thought college life would give him a fresh start. You thought that he would have the coping skills to live alone? I thought that by putting him out there -- and giving him Independence and integrating him into a Normal society would very quickly help develop the skills that I thought was lacking in him. Did you inform anyone either at the college or the parents of his roommates that he had mental problems? I didn't see any reason to because as far as I was concerned he wasn't a threat to himself or anybody else. Reporter: But left to his own devices, Elliot Rodger's behavior would soon escalate from strange to savage. Simon astaire is a longtime friend of peter's. I got the sense of a boy who was unable to communicate. So that there were signs, you thought, of maladjustment? He was unable to engage and it was difficult to engage. And I saw loads of people trying to engage with him. Reporter: But soon, the old resentments would return. Enraged by the sight of young lovers, he acted out for the first time -- throwing coffee on one kissing couple at Starbucks. I had never struck back at my enemies before, and I felt a small sense of spiteful gratification for doing so. Reporter: Feeding on that fulfillment, his thoughts began to take a more diabolical and dangerous turn. "The day of retribution" had been born. It was only when I first moved to Santa Barbara that I started considering the possibility of having to carry out a violent act of revenge, as the final solution to dealing with all the injustices I've had to face at the hands of women and society. Reporter: His anger, now targeted at women, drew him to misogynistic websites -- online forums where he once wrote, "Start envisioning a world where women fear you." He sent you links to these websites. I was disgusted. And I called him up and I said, "Elliot, why are you going on these websites? This is negative, this is -- evil. And you shouldn't go on there." That didn't work? It didn't work. And I had no idea that he had such an imbed hatred, this misogyny. Reporter: But despite his deepening hatred of women, Elliot told his father he was obsessed about losing his virginity. I would say to him, there is no shame at all in not losing your virginity at a later age. Some people never do. Some people go into the church and choose chastity." And he would say, "I can't get a girlfriend"? He did say to me once I wish I wasn't half asian. I never realized that he was so racist. Thinking, "Why aren't I white?" Correct. Reporter: Elliot's life had become a volatile mixture of desire and denial. And last summer, yet another sign of violence. Frustrated after being ignored by girls at a party, he tried to shove them off a ten-foot ledge. He got into an altercation verbally with a couple of girls. And then he was picked on and then he was thrown off a balcony. But it turns out that he was trying to push girls off the ledge? In 20/20 hindsight, I can imagine that might have been the case and that upsets me to the core of my heart. He was such a good liar. He was such an incredible liar. Reporter: Perhaps Elliot was even lying to himself. Repeatedly refusing the advice of therapists at least one of whom had recommended medication. But Elliot would say, "I'm not sick. I'm not going to take that." And because he was of an adult age, he refused to not only take that medication, but refused to go back to see that particular doctor. Would the medication have made a difference? According to his doctor it would have made a hell of a lot of difference. There are people who say that a father with a mentally unstable son should not have allowed Elliot to live on his own. I didn't know I had a mentally ill son. I had no idea. He had a secret life that he became incredibly brilliant at hiding. Hey, Elliot Rodger here. Reporter: But that secret life was spinning out of control. Here's me in all my fabulousness. Reporter: With no official diagnosis of mental illness, he bought not one not one, but three handguns. Elliot had launched his plan for retribution day. As I fired my first few rounds, I felt so sick to my stomach. There I was, practicing shooting with real guns because I had a plan to carry out a massacre. Why did things have to be this way? This is my place of refuge. Reporter: Then a pivotal moment when Elliot's plot might have been completely foiled. His mother finding one of those bizarre videos on youtube. My life is so lonely and mundane. She wanted to have a mental assessment of him. It just turns out that there is no way that you can actually do that unless he voluntarily does it or unless he commits a crime. Did Elliot volunteer? Would he have done it? No. He didn't? Of course not. She alerted the police, yes, and what happened? Six officers arrived at Elliot's apartment and knocked on the door. And Elliot was a very, very polite, kind, well-spoken, well-dressed individual. And he managed to say, "You've got nothing to worry about." If they had demanded to search my room that would have ended everything. For a few horrible seconds, I thought it was all over. Reporter: But the police neither watched the youtube videos nor ran a background check for purchasing guns. And this is where the system I think failed. If somebody's going to do a welfare check, surely they should do a gun check on the way. Because how is somebody going to do something to themselves if they don't -- if they feel they're a danger? It takes 90 seconds to do a gun check. And his whole scheme would've been over and thwarted. I want to make something very clear, Barbara. I'm really not pointing any fingers at the Santa Barbara police department. Reporter: That was the turning point between life and death. A missed moment that began the countdown to Elliot's day of retribution. Well, this is my last video. It has all come to this. The day in which I will have my revenge against humanity, against all of you.
This transcript has been automatically generated and may not be 100% accurate.