But his mother was not allowed to enter his bedroom, according to the report, and it was not clear how much she knew about his obsession.
While the details released Monday led some observers to direct their anger at her, suggesting she was more enabler than victim, others were more sympathetic.
A friend of Nancy Lanza's, Marvin LaFontaine, said that she was a devoted mother to her two sons and that she showed up at Adam's elementary school to protect him when he was picked on by other children.
"She lived for her kids. I thought she was a wonderful parent. She would have done anything for those kids," LaFontaine said in a recent interview.
Lanza, 20, shot his mother in the head four times Dec. 14, then drove to Sandy Hook Elementary School, where he killed 20 first-graders and six women with a semi-automatic rifle. He committed suicide as police arrived.