SOUTHBURY, Conn. — At Newtown High School, Adam Lanza had trouble relating to fellow students and teachers, but that was only part of his problem. He seemed not to feel physical or emotional pain in the same way as classmates.

Lanza is the gunman that killed 20 children and 6 adults before killing himself at a Connecticut elementary school on Friday.

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 with school guidance counselors, administrators and with the boy’s mother, Nancy Lanza, 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.

Adam 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.”