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.
The report released Monday by the lead investigator, State's Attorney Stephen Sedensky III, detailed some of the family's efforts to address the needs of a young man described as withdrawn, lacking an appreciation of other's feelings, and beset with "significant mental health issues."
He had evaluations of many types over the years, he was home-schooled for a period because he did not like the noise at Newtown High School, and he refused medications and behavior therapies that were suggested for him.
Some parents of other troubled young adults said they can understand what Nancy Lanza was going through.
Peggy Sinclair-Morris, a special education teacher in Midlothian, Va., said it was like the "wild, wild west" as she tried to find the right treatment for her 18-year-old daughter, who has an anxiety disorder and has attempted suicide several times. If your child does not have certain symptoms, she said, you can get passed around by the system.
"I feel empathy for his mom just because, like I said, you try to find the services and when they're not available, you try to do what you have to do to help your kids," Sinclair-Morris said. "Just because your son committed that horrible act doesn't mean she was a horrible mother."
Nancy Lanza, who was divorced from Adam's father, indicated that she did not work because of her son's condition. In their spacious Newtown home, she catered to his requests, cooking to his specifications and getting rid of a cat because he did not want it in the house.
In the weeks before the massacre, she said he hadn't gone anywhere in three months and that they would communicate only by email, even though they lived under the same roof.
She often took her soon shooting at a gun range. She legally purchased all of the weapons that her son carried the day of the massacre, and she had written a check to buy him a pistol for Christmas.
The report said that she was concerned about her son, but that she never expressed fear that she or anyone else was in danger from him. He was never violent or threatening toward others before the attack, according to the report.