He rarely spoke and even gave a school presentation entirely by computer, never uttering a word.
He liked tinkering with computers and other gadgets, and seemed to enjoy playing a violent video game, choosing a military-style assault rifle as one of his weapons.
New details about Adam Lanza emerged Friday, as the nation paused to mark one week since he slaughtered 20 first-graders and six adults at Sandy Hook Elementary School in Newtown.
Multiple funerals and visitations were held Friday, and at the hour of the attack, 9:30 a.m., a bell tolled 26 times, once for each victim killed at the school.
Lanza also fatally shot his mother before blasting his way into Sandy Hook, and killed himself after the school massacre.
In high school, Lanza would walk through the hallways, awkwardly pressing himself against the wall while wearing the same green shirt and khaki pants every day. He hardly ever talked to his classmates.
"As long as I knew him, he never really spoke," said Daniel Frost, who took a computer class with Lanza and remembered his skill with electronics. Lanza could take apart and reassemble a computer in a matter of minutes
Lanza seemed to spend most of his time in the basement of the home he shared with his mother, who kept a collection of guns there, said Russell Ford, a friend of Nancy Lanza's who had done chimney and pipe work on the house.
Nancy Lanza was often seen around town and regularly met friends at a local restaurant. But her 20-year-old son was seldom spotted around town, Ford and other townspeople said.
The basement of the Lanza home had a computer, flat-screen TV, couches and an elaborate setup for video games. Nancy Lanza kept her guns in what appeared to be a secure case in another part of the basement, said Ford, who often met her and other friends at a regular Tuesday gathering at My Place, a local restaurant.
During the past year and a half, Ford said, Nancy Lanza had told him that she planned to move out West and enroll Adam in a "school or a center." The plan started unfolding after Adam turned 18.
"She knew she needed to be near him," Ford said. "She was trying to do what was positive for him."
Ford said Nancy Lanza didn't elaborate on what type of services she wanted her son to receive. He said she made fewer appearances at the restaurant in recent months.
Mark Tambascio, owner of My Place, said Nancy Lanza described the same plan to him, saying she might move to Washington State.
Back in high school, Frost recalled, someone brought in a video game called "Counter-Strike," a shooting video game in which players compete against each other as either terrorists or counter-terrorists.
Lanza "seemed pretty interested in the game," Frost said, and would play it with other students. He remembers the weapons Lanza chose: an M4 military-style assault rifle and a Glock handgun.
Authorities said Lanza used a military-style assault rifle and carried handguns during the rampage at the school. They still have no clear reason why Lanza would lash out at defenseless first-graders and their caretakers.
State police spokesman Lt. J. Paul Vance said a final report on the investigation could be months away.
A moment of silence was held Friday in remembrance of those killed at the school. Gov. Dannel P. Malloy gathered with other officials in rain and wind on the steps of the Edmond Town Hall as the bell rang. Similar commemorations took place across the country.
Also on Friday, the National Rifle Association called for armed police officers to be stationed at schools. Wayne LaPierre, CEO of the nation's largest gun-rights lobbing group, said at a Washington news conference that "the only thing that stops a bad guy with a gun is a good guy with a gun."
LaPierre blamed video games, music and videos for exposing children to violence.
The founder of a video game website said he expects tens of thousands of players of online shooter games to participate in a 24-hour cease-fire that started at noon Friday. Antwand Pearman, founder of GamerFitNation, said the cease-fire is meant to show respect for those killed in the Newtown shooting. He said video games don't cause violence.
Associated Press writers Matt Apuzzo in Washington and Pat Eaton-Robb in Newtown contributed to this report.