Why Did Adam Lanza Snap?

Part 2: Shooter was "a little bit different - kind of repressed."
4:33 | 12/14/12

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Transcript for Why Did Adam Lanza Snap?
And that takes us to our chief investigative correspondent brian ross, trying to understand this young man and the troubles that led him to this hosht act. Brian? He was arnled with guns and went from on curety to infamilymy. He was known as someone who do not play well with others. The perp rater of the crime is dead. A little different. Unfortunately, what's in the mind of that shooter now, he's taking to the grave with him. Tonight, no one yet seems to be able to answer the question, why 20-year-old adam lanza, seen here in a photo provided to abc news from seven years ago, attacked the newtown elementary school. We will go backwards as far as we have to go and hopefully stumble on answers. Adam lanza was the child of an affluent connecticut town and a child of divorce. In morning, he first killed his mother, nancy. Family friends bash ka frey told jim avila the son was troubled and the family was demandsing of him. He was not connected. My son played with him when they were young. In her home, she was very particular. I just think she maybe had too high of a standard of something. Or focused too much for whatever reason. So was there conflict? Was there tension between the two of them? The parent and the child? I don't think so. The pants were divorced. The young man headed to the sandy hook elementary school wearing a bullet proof vest. Authorities say he was armed with a semiautoic assault rifle and two pistols. A relative says that adam was not well. The important thing, he did not just snap this morning and decide to act out violently. These crimes involve plans and strategizi strategizing. Why the attack on the children at the school. Most of them killed on the spot, according to authority. His mother, divorced three years ago and unemployed and worked as a teacher's aide at the school. The children, his mother may be the real focus on this, the anger and rage and resentment has built up over the years and he decided, I am been powerless all this time. So far, it's only a theory following a day on confusion. Starting with state and federal authorities wrongly identified the shooters a adam's brother, new york accountant. That led to him saying, I wasn't me. I was at work. It wasn't me. When ryan arrived at his home in hoboken, new jersey, police took him in for questioning. They spent the evening at a police stations a authorities seek fought he had any dwlad adam was trying to be violent. They are trying to say, yes, he said that, I thought he was joking. Couldn't believe that anyone would do that. I just ignored that. It's not known if adam lanza made any such threats. The end, he apparently killed himself after killing so many others. What they say is the outcome in cases like this one. They know when they go they with going to guy at the scene in the hanth ohe police or they kill themselves. Police know in horrifying detail what happened in the school but they don't know what happened inside the damaged mind and broken soul of adam lanza.

This transcript has been automatically generated and may not be 100% accurate.

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