FBI documents: Massacres 'fascinated' Newtown gunman

The FBI released more than 1,500 pages of documents related to its investigation of the massacre at the Sandy Hook Elementary School in Newtown, Connecticut, in 2012.

The FBI documents offer a window into the early days of the investigation. People told the FBI that shooter Adam Lanza had become a "shut in" and a "recluse" and that his mother, Nancy, had become concerned about him a month before the mass shooting because he hadn't gone anywhere in three months. They said he stayed in his bedroom and played video games all day.

A woman told Connecticut State Police her son was playing the video game "Call of Duty: Black Ops" with someone the day before the shooting who told her son to "watch the news tomorrow."

On December 14, 2012, Lanza shot and killed his mother in their home while she was sleeping. Then he went to Sandy Hook Elementary School and killed 20 first-graders and six educators.

Most of the information in the FBI documents has been redacted, including the names of the people who spoke with the FBI. Some said Lanza had no friends, was computer-savvy, and loved guns. Others called his mother a "gun nut" who taught her son how to fire a gun and took him to shooting ranges.

Mental health experts concluded in 2014 that Lanza was on the autism spectrum and had psychiatric problems but said those health issues did not cause or directly lead to the massacre.

The FBI documents released Tuesday also included a statement from someone who knew Lanza and said: "Nancy never let anyone come into her home. If one of the neighbors was picking up Adam, Nancy would tell them to wait in the driveway."

Another said his mother would take care of Lanza's needs, "however, she never cleaned his room, nor was allowed in his room. Adam's room was his personal space that no one else was allowed into."

Another Newtown resident said Nancy had told them that Lanza had once hacked into a government computer system and federal agents showed up at their house. She had to convince them that he didn't mean any harm, that he was just intelligent, and was challenging himself.

A year after the massacre, state police released a final report that concluded Lanza was obsessed with guns, death, and mass shootings.

Lanza's motive for the shootings is still is not known.