Adam Lanza: Who Was Elementary School Shooter?

Brian Ross reveals what authorities have uncovered since deadly attacks at Sandy Hook elementary.
2:41 | 12/17/12

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Transcript for Adam Lanza: Who Was Elementary School Shooter?
New detail this is morning about the gunman. We're piecing together a picture of adam lanza. Still left with the question of why? Why would he target such small children. Brian ross has been tracking that part of the story since the beginning. What have you learned? Reporter: Good morning, elizabeth. Authorities say they expect more progress today as they figure out the how and the why of what happened. Veteran ajtss are ha-- agents are having hard time at the scene. He had a huge quantity of bullets left for his high-powered weapons. All weapons have multiple magazines and additional ammunition. Reporter: As to his motive, officials tell abc news that computers taken from the home over the weekend provide clues to his twisted thinking. It was here he killed his first victim, his mother, 52-year-old nancy lanza, who friends say was more and more concerned about adam's issues over the last few months. It was harder for her as time went on, as he was getting through school. Reporter: Adam's parents were divorced three years ago. His mother was left to deal with him alone, according to her friends. She took care of it the best she could. Reporter: Since elementary school at sandy hook until his mother home-schooled him, he was known as odd. He hated to look into your eyes for more than a few seconds. Reporter: He was a member of the tech club. And the school's former security director says the young man could feel neither emotional nor physical pain. If he cut himself or hurt himself, he would not know it or feel it. Reporter: He says lanza had several disorders and was seeing the school psychologist. He had periods of time where he would withdraw entirely. You would have to work hard to reach him again. Reporter: Police this morning say when he killed his first victim, he used the awe salt-style rifle to kill her with several shots to the head. A gun she owned legally. Your expert in the piece saying he didn't feel physical pain. Makes you won't per that means he didn't feel motion nal pain as well. We'll be delving into that in

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

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