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Adam Lanza Got Guns From Gun Owning Mother

Brian Ross investigates Sandy Hook gunman's access to deadly weapons.
2:15 | 12/16/12

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Transcript for Adam Lanza Got Guns From Gun Owning Mother
And we are getting a more complete picture of the gunman as police try to learn more about why 20-year-old adam lanza went on his bloody rampage. Abc's chief investigative correspondent brian ross is here with the latest. Brian, you're happening the weapons he used were likely licensed to his mother who is described as a gun enthusiast. Correct according to people on the scene. Authorities are moving with more developments likely to come today in their efforts to determine the how and the why of this stunning crime. Police say they have already found important clues in their home where the killer's mother, 52-year-old nancy lanza was the first victim. Hopefully painting the complete picture as to how and more importantly why this occurred. Reporter: Authorities now say nancy lanza owned the same style of guns that her son used to kill her and the 26 victims at the elementary school. The medical examiner said most were killed with multiple shots from the high-pourered semiautomatic rifle. This is probably the worst i have seen. The connection between adam lanza and the sandy hook elementary school goes back to the time he went to school there and his mother worked as a teacher's aide. According to add gam's aunt. I know she had issues with school. She eventually wound up home schooling him. She battled with the school district and what took place I'm not 100% certain if it was behavior. Reporter: As a fuller picture of adam lanza began to emerge including his membership in the tech club, he was a smart but socially awkward student. He always carried a briefcase. Reporter: Adam's parents peter and nancy lanza went through an uncontested divorce and adam's aunt said that nancy had purchased so many weapons because she was concerned for her safety living alone. I think no reason why nancy may have had them for self-defense and no other reason. Reporter: Friends have told us that nancy lanza enjoyed taking her sons to the firing range for practice. She could have been there when he was learning how to shoot those guns.

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

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