One week ago on our broadcast, a watershed moment. The first time the father of a pass murderer spoke on national television. Peter Rodger told us his son was mentally ill, but didn't think he would... See More
One week ago on our broadcast, a watershed moment. The first time the father of a pass murderer spoke on national television. Peter Rodger told us his son was mentally ill, but didn't think he would be capable of such violence. You felt very strongly about what you saw. And now, tonight, what you told us. Words of wisdom. Of power. And hope. Of the hundreds of posts on our Facebook page, there were five words that were used more times than any others. Help. Parents. Mental. People. Father. A kind of mantra that made us wonder about the good that can come out of tragedy. Reporter: There have been numerous school shootings. And none of the parents of other shooters have spoken with us. Why did you decide that you would speak out? Because we have to stop this, Barbara. This is wrong. Wrong. Wrong. And there are too many fingers pointed in the wrong directions. We need to mend the mental health thing. I think that there's an awful lot that can be done in this country to help families that might have another Elliot. Reporter: Among those hundreds of posts, we found parents walking the same path of fear and despair. I'm almost scared to go to sleep after watching this. I have an almost 17-year-old in my home who is just like this kid. Yet no one will help. I wish our world would wake up and realize we have to change our view on these types of mental illnesses. No parent wants this for their child. No parent wants to live in hell of tears of not knowing what to do, where to go. Reporter: If there is an illness, if there's cancer in a family, people rally around. With mental illness, they don't. I think mental illness is a big elephant in the room right now and this country needs to get up, wake up, and look at it. Reporter: Peter Rodger's son, Elliot, was only 22 when he died, taking six other lives with him. The videos and so-called manifesto he left behind provided a rare glimpse into a mind broken by mental illness. I don't know why you girls aren't attracted to me. But I will punish you all for it. Reporter: What's the most shocking revelation to you? That he could hide. That he could hide these feelings from everybody. I can't wrap my head around it. It's extremely difficult to predict future violence. People have spent their careers looking at ways to predict violent behavior. And we're terrible at it. Really the only prediction of future violence is past violent behavior. Again, in this case there was apparently no evidence of that. Reporter: But inside that shy, quiet young man was hidden rage. Elliot's journal documented a master plan of revenge, once writing, "If I can't have it, I will destroy it." Andrew Solomon has studied the patterns between mass murderers at columbine and Newtown. In neither instance was the mass killing something that happened on the spur of the moment. It was something imagined and it was imagined in each instance as the moment of their getting revenge on a world that had rejected them. Reporter: For peter Rodger, in retrospect, the clues seemed so clear. But he, like many parents, he seemed to miss them all. Reporter: You feel now that there are warning signs. Tell me the warning signs. A young man between the age of 18 and 22 who is socially inept, doesn't have any friends, finds it difficult to get a girlfriend, spends far too much time on the computer, is narcissistic. I'm such a magnificent guy. Constantly taking photographs of themselves. There's me. Illusions of grandeur. These are the traits that -- I think are really important for the American people to understand. Reporter: But even if he had recognized the warning signs, there was nothing Rodger could have done after his son turned 18 and became an adult. This father realized there was something wrong, tried to get help but was helpless due to his child's age. You can't judge unless you've been in their shoes. I wonder how easy it is to physically take a mentally deranged individual to a hospital when they are not willing to go? How can parents diagnose or treat a son who won't take prescriptions? Reporter: Would the medication have made a difference? When somebody is over 18, and they refuse medication, it is impossible for you as a parent or a family member to make them take that medication, unless they do it voluntarily or if they commit a crime. The mental health community have to work out some kind of middle ground to be able to help family members who think that they -- an adult family member might be a risk to themselves or to somebody else. Reporter: You have said that you're going to spend your life, to raise awareness for other families who live with children who are mentally ill. How can you do that? By telling Elliot's story. Asking families to understand, love and support children that might be in the same position as Elliot. He was my best friend. It wasn't Elliot taking his own life. He took the lives of other people. And he injured other people who are gonna have scars for the rest of their life. I have so much compassion for them. I feel if only, if only, if only. But I don't think there are any if onlys. To help other families like his, he has created a website called ask for Summer
This transcript has been automatically generated and may not be 100% accurate.