Long before Lanza's spree residents of Newtown had noticed that tall, pale boy was different, and believed he had some kind of unspecified personality disorder.
"Adam Lanza has been a weird kid since we were five years old," wrote a neighbor and former classmate Timothy Dalton on Twitter. "As horrible as this was, I can't say I am surprised."
In school, Lanza carried a black briefcase and spoke little. Every day, he wore a sort of uniform: khakis and a shirt buttoned up to the neck, with pens lined up in his shirt pocket.
A former classmate in his 10th grade honors English class, Olivia DeVivo, says he "was always very nervous and socially awkward."
She told ABC News that "he didn't really want to be spoken to" and that when teachers would call on him "it appeared physically difficult for him to speak."
Lanza avoided public attention and had few, if any, friends, though he was a member of the high-school tech club. He liked to sit near the door of the classroom to make a quick exit.