At Newtown High School, Adam Lanza had trouble relating to fellow students and teachers, according to various witnesses, but that was only part of his problem.

He seemed not to feel physical or psychological pain in the same way as classmates, a former employee at the school said.

Richard Novia, the school district’s head of security until 2008, who also served as adviser for the school technology club, said Lanza clearly “had some disabilities”.

“If that boy would’ve burned himself, he would not have known it or felt it physically,” Novia said. “It was my job to pay close attention to that.”

Novia was responsible for monitoring students as they used soldering tools and other potentially dangerous electrical equipment.

He recalled meeting school guidance counsellors, administrators and the boy’s mother, Nancy, to understand his problems and find ways to ensure his safety. But there were other crises only a mother could solve.

“He would have an episode, and she’d have to return or come to the high school and deal with it,” Novia said, describing how the young man would sometimes withdraw completely “from whatever he was supposed to be doing”, whether it was sitting in class or reading a book.

Lanza “could take flight, which I think was the big issue, and it wasn’t a rebellious or defiant thing”, Novia said. “It was withdrawal.”

Authorities are trying to understand what led the young man to kill his mother in their home and then slaughter 26 children and adults at the Connecticut elementary school before taking his own life.

A law enforcement source said Lanza was diagnosed with Asperger’s, a mild form of autism. People with the disorder tend to function poorly socially but can be highly intelligent.

If he did have Asperger’s, his lack of sensation could be related to the disorder, said psychologist Elizabeth Laugeson, an assistant clinical professor at the University of California, LA. People with Asperger’s can be overly sensitive to things like touch, noise and pain, or sometimes under-sensitive, she said.

Back in their teenage years, Lanza and his older brother, Ryan, were members of the technology club, which offered students a chance to work on computers, videotape school events and produce public access broadcasts.

Lanza, while clearly smart, had problems that went beyond an adolescent lack of social skills, Novia said: “You had a very scared young boy, who was very nervous around people.”

The club provided a setting for students to build lasting friendships. But while other members were acquainted with Lanza, none was close to him.

He was not physically bullied, although he might have been teased, Novia said.