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The law enforcement officials insisted on anonymity because they were not authorized to discuss the unfolding investigation.

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

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

Contributing to this report were Associated Press writers Jim Fitzgerald, Bridget Murphy, Pat Eaton-Robb, David Klepper and Michael Melia in Newtown; Denise Lavoie in Danbury, Conn.; Adam Geller in Southbury, Conn.; Stephen Singer in Hartford, Conn.; Pete Yost in Washington; and the AP News Research Center in New York.