The Sandy Hook school shooter had Asperger's syndrome and skipped his medications, according to details within hundreds of pages of documents on the incident released by the FBI.

Much of the information is redacted to protect people's identities, but News 12 is learning there were some clues beforehand that the shooter, Adam Lanza, might do something violent.

Lanza killed 26 people, 20 of them children, at Sandy Hook Elementary back in 2012, less than two weeks before Christmas. He also killed his own mother a short while earlier.

The documents describe him as a loner who didn't leave his house for three months before the mass shooting -- but the FBI says he was talking to people online during that time.

One of his contacts was a woman who told investigators she had spoken with Lanza for two years over the internet. She told agents that he kept a spreadsheet to track details behind hundreds of mass murders.

"(Lanza) was focused completely on spree killings and mass murders," she told them, because he may have believed he was protecting the victims from adults who he believed "were inappropriately controlling children."

Another woman told the FBI that Lanza went on a suicide website days before the shootings. She told investigators that he planned to kill himself and warned that it would be in the news. She also told agents that he might have prepared for the shooting with the help of a YouTube video.

And the mother of an online gamer told Connecticut State Police that her son was playing "Call of Duty" with an individual who told him to "watch the news tomorrow."

Another man told investigators that Lanza had threatened Sandy Hook four years before the shooting because his mother, who once volunteered there, "loved the students more than she loved him."