Mom Taught Lanza to Shoot

Profiler: "I think that gun empowered him."
3:00 | 12/17/12

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Transcript for Mom Taught Lanza to Shoot
As the nation struggles to come to terms with the tragedy that struck sandy hook elementary school, new details are emerging about the 20-year-old shooter. Tonight abc news confirmed that his parents have been separated since 2001 and he had not spoken to his father or older brother in the last two years. Abc's chief investigative correspondent brian roth has the latest. Reporter: In the last month of adam lanza's life family and friends say he would not leave the house. With his mother nancy, telling them she was losing control of her 20-year-old son. It was getting harder for her as time went on. Reporter: Nancy lanza was a regular at newtown bar and restaurant, my place where the owners say she told them about her struggles with adam's emotional and behavior problems for years. She was helping him all the time. She home schooled him and everything. So she, you know, I knew he was on medication but that'sll i know. Reporter: Since her divorce from peter three years ago, her friends say nancy was left to deal with adam by herself. We knew he had a problem. But she took care of it the best she could. She was a single mom. Reporter: Since elementary school at sandy hook, through high school, adam was known as strange, severely shy. He hated at lookling at your eyes for more than a couple seconds. It made him feel uncomfortable and he made you feel uncomfortable as well. Reporter: A former babysitter said he was told never to leave him alone. Nancy told me to never turn your back on him at any time. Reporter: The former school security director says that he was seeing the school psychologist. If he cut or hurt himself he would not know it or feel it. We were careful with him. Reporter: On friday, the shy adam turned into a different person and now the mystery of why is at the center of the police investigation. We will answer every single question, determining any kind of medical condition, any kind of issue whatsoever that may have been involved in. I'm not at liberty to discuss medical content or any of the information so far uncovered. Reporter: One big question is why his mother, knowing of his emotional issues introduced adam to the world of high-powered guns including the semiautomatic bushmaster rifle that he used in his deadly rampage that she bought legally in march 2010. Agents say mother and son went to the firing range together in the last six months. You have a child that is troubled and doesn't bond with people or with her, apparently and you introduce something that is so lethal and violent if appropriately used it's an extremely poor decision on her part. Reporter: Especially with the bushmaster one of the most popular guns in the country, demonstrated in a video posted on the company youtube channel. It can fire 45 rounds in a minute and modifies so it is legal even under the connecticut law meant to ban the weapons. If you go to their website they have a page called state compliant. But it is still just as deadly. It makes it dangerous of course is the ability to take unlimited amounts of ammunition in the pistol grip. Reporter: On friday adam showed up at the school with the bushmaster and two handguns and hundreds of bullets, enough to kill everyone, every student and children only the sound of approaching police stopped him. That gun empowered him. Once he decided to commit the shooting he has now been trained with a piece of equipment that will accomplish that. Reporter: Police and federal agents are working on another key piece of evidence, a computer hard drive found in the lanza home. Someone tried to destroy it with a hammer or screwdriver. Agents say it will not stop them from recovering what was on the hard drive, perhaps the secret that adam lanza wanted no one to

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

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