Adam Lanza
Adam Lanza is pictured in this undated handout photo courtesy of Western Connecticut State University. Reuters

The Federal Bureau of Investigation (FBI) on Tuesday released 1,500 pages from its investigation into the Sandy Hook Elementary School shooting massacre that took place Dec. 14, 2012 in Newton, Connecticut. Adam Lanza, 20, was said to have fatally shot 20 children and six adult staff members in one of the worst shooting incidents at a school in the United States.

Records pointed to evidence that suggested Lanza, who had killed himself when police arrived at the school following the mass shootout, was planning the attack from March 2011.

The documents released included interviews conducted by the FBI agents with the people who knew Lanza. Several portions of the documents that have names of people have been redacted. The records also reflect upon the initial stages of the investigation, The Guardian reported.

In the documents, there is a mention of a woman who befriended Lanza online before the 2012 Sandy Hook rampage. She said Lanza was "singularly focused and obsessed with mass murders and spree killings." Lanza also looked upon school shooters "with respect and understanding," according to CNN.

The woman described Lanza as "the weirdest person online" who seemed to devote almost all of his Internet activity to researching and discussing" mass killings he documented and viewed as "a symptom caused by a broken society," the documents said.

The woman also told investigators that the 20-year-old shooter was "extremely intelligent," however he was also depressed and cynical and mostly had a negative view of the world.

The woman said Lanza's online posts and messages hinted at him being functionally depressed. As far as she knew, Lanza did not have an effective coping mechanism to deal with his depression. "He seemed to wallow in it and ride out the low periods by hiding in his room and sleeping for 12 hours or more at a time," the records stated.

On July 29, 2014, investigators released results of a behavioral analysis of Lanza, which suggested he was a pedophile. Those results were released to law enforcement and victims' family members, USA Today reported.

During the investigation, it was revealed that Lanza's deteriorating relationship with his mother, Nancy Lanza, could have contributed to his stress levels in the weeks before the attack. But the behavioral analysis also found that Lanza did not "snap." He engaged in "careful, methodical planning and preparation" for the attack, according to FBI.

The FBI also found, from Lanza's neighbors, that years before the Sandy Hook shooting incident, Lanza had apparently hacked into a government computer system when he was in ninth grade. Law enforcement agents had also visited Lanza's home.

Nancy had told about it to neighbors at a party and said her son had made it to the second level of security on the government site, but the third layer of security was able to thwart his hack.

Nancy also told the FBI officials that her son was extremely intelligent and that he was trying to challenge himself. The agents told Nancy that someday, her son could have worked with the FBI if he was so smart.