He carried a black briefcase to his 10th-grade honors English class and sat near the door, so he could readily slip in and out. When called upon he was intelligent but nervous and fidgety — spitting his words out, as if having to speak up were painful.

Pale, tall and scrawny, Adam Lanza walked through Newtown High School with his hands glued to his sides, the pens in the pocket of his short-sleeve, button-down shirts among the few things that his classmates recalled about him.

He did all he could to avoid attention, it seemed.

Until Friday, when authorities said Lanza, 20, carried out one of the deadliest school shootings in the nation’s history.

In his brief adulthood Lanza had left few footprints, electronic or otherwise. He apparently had no Facebook page, unlike his older brother, Ryan, a Hoboken, N.J., resident who for several hours on Friday was misidentified in news reports as the perpetrator of the massacre.

Adam Lanza did not even appear in his high school yearbook, that of the class of 2010. His spot on the page said "Camera shy."

Lanza did belong to a technology club at school that held "LAN parties" — short for local area network — in which students would gather at a member’s home, hook up their computers into a small network and play games, The Associated Press reported.

Matt Baier, now a junior at the University of Connecticut, and other high school classmates recalled how deeply uncomfortable Lanza was in social situations.

Several said in separate interviews that it was their understanding that he had a developmental disorder. They said they had been told that the disorder was Asper­ger’s syndrome, which is considered a high-functioning form of autism.

"It’s not like people picked on him for it," Baier said. "From what I saw, people just let him be and that was that."

Law enforcement officials said Friday that they were closely examining whether Lanza had such a disorder.

Out of view of his classmates, Lanza’s adolescence seemed to have been turbulent. In 2006 his older brother graduated high school and went to Quin­nip­iac University in Connecticut, leaving him alone with their parents — whose marriage was apparently coming apart.

In 2008 they divorced after 17 years, court records show. His father, Peter Lanza, a tax executive for General Electric, moved to Stamford, and remarried in January 2011.

His mother, Nancy Lanza, kept their home in Newtown about five miles from the elementary school where she worked. Adam Lanza is thought to have been living in the house, too.

Friends remembered Nancy Lanza as being very involved in her sons’ lives.

"Their mother was very protective, very hands-on," said Gina McDade, whose son was a playmate of Ryan Lanza’s.