Newtown Elementary School Shooter Details

Gunman, identified as Adam Lanza, 20, was armed with two handguns and found dead inside school.
4:29 | 12/15/12

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Transcript for Newtown Elementary School Shooter Details
Senseless unthinkable -- conceivable there are no shortage of words to describe the tragedy that struck. At the elementary school right here in Newtown Connecticut today but we've heard one word repeated over and over again. Why. ABC's chief investigative reporter Brian Ross -- spent the day uncovering details about the twenty year old -- Brian. Cynthia he was armed to the teeth was legally purchase guns and went from obscurity to infamy. Until today Adam -- it was known mostly as neighborhoods that someone who did not play well with others. Adam lands it was a child of an affluent Connecticut town and the child of divorce story a family friend Barbara -- Told ABC's -- apple that the sun was trouble and the mother include demanding. It was not connected. With other kids. My son played with him when they were young. And in her home -- she was very particular. If you think she. And maybe has two highest standards. Just four. Focused believe too much for whatever reason. So it it was their conflict was -- was or some kind of tension between the two of them. The parent child and grandchild -- not that I know of but I think the fact that the parents were divorced must have contributed to that. Tonight Adam's brother Ryan and his father Peter GE tax -- were questioned by the FBI and police in New Jersey. Looking for clues as to what led the youngest member of the family to kill. Someone believed to be -- lands -- left the station tonight without comment. I think the most important thing to point out with this kind of an individual is that. He did not snap just this morning and decide to act out violently. These crimes involve -- -- and fought illness and strategizing. In order to put the plan together. So what may appear to be snapped behavior. It is is not bad at all and. After first killing his mother -- the family home authorities say the young man headed to the sandy hook elementary school wearing a bulletproof vest. Authorities say he was armed with a semiautomatic assault rifle. And two high powered pistols like these police say both his mother and his father legally owned a number of guns of the same kind. A relative said Adam was obviously not well. We'll go backwards as far as we have to go. In this investigation and and and hopefully we'll stumble -- answers. But what even the crime profile as are having a hard time trying to figure out -- -- is why the attack on the children. Most of them killed on the spot according to authorities. The only theory is based on reports that his mother divorced three years ago an unemployed may have worked as a teacher's aide at the school. The children didn't harm him but they are associated with his mother. In his mother I believe in May be the real focus of all of this the anger and rage and resentment has built up in him over a number of years. And he decided I've been powerless all this time and now I'm going to empower myself. But so far it is only a -- following -- day of confusion and misinformation about the tragedy. Starting when state and federal authorities first identified the shooter as Adam's older brother Ryan now a New York accountant. That led to Ryan posting messages on his FaceBook page it wasn't me I was at work it wasn't -- -- But when Ryan arrived at his home in Hoboken, New Jersey police took him into custody for questioning. Authorities want to know if -- or anybody else in the family had any idea Adam was threatening to become violent. Typically I've heard people say yes he set that but I didn't take him seriously. Yes he said that I thought he was joking I couldn't believe that anyone would do that I just ignored him. It's not known -- Adam -- -- made any such threats in the end he apparently killed himself at the school after killing so many others. What crime profiler say is the expected outcome in cases -- -- Everyone -- won't either they know when they go that they're gonna die at the scene either by the hands of the police or -- kill themselves. Police know in horrifying detail what happened inside that school but they don't yet have any idea what happened inside the it's mind and broken soul of -- --

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

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