By Marc Santora

New York Times News Service

Peter Lanza had not seen his son Adam for two years before the day Adam walked into Sandy Hook Elementary School in Newtown, Conn., and killed 20 schoolchildren and six adults.

Since that morning, Lanza cannot go an hour without thinking about his child. And now, he says, he wishes his son had never been born.

“You can’t get any more evil,” he said in his first public comments since the shooting. “How much do I beat up on myself about the fact that he’s my son? A lot.”

In a series of emotionally wrenching interviews with the writer Andrew Solomon, Lanza detailed his son’s medical history and increasing isolation, his ex-wife’s struggle to deal with their troubled child, and his own role as the father of the person who committed one of the worst mass shootings in the nation’s history.

Solomon, the author of the book “Far From the Tree: Parents, Children and the Search for Identity,” recounts the interviews in an article in this week’s issue of The New Yorker magazine.

Adam Lanza, 20, shot his mother, Nancy, before going on his shooting rampage at Sandy Hook on Dec. 14, 2012, and then shot himself just as the police were arriving at the elementary school.

Peter Lanza said he had no doubt that his son would have killed him as well.

“With hindsight, I know Adam would have killed me in a heartbeat, if he’d had the chance. I don’t question that for a minute,” he said. “The reason he shot Nancy four times was one for each of us: one for Nancy, one for him, one for Ryan, one for me.”

Ryan is Adam’s older brother.

An exhaustive report by Connecticut authorities released last year provided the most complete picture to date about Adam Lanza’s life and the events on the day of the shooting.

Peter Lanza’s account confirms the basic portrait that emerged from the investigation, and adds new details as well as a deeper understanding of how he and Adam’s mother struggled to understand and care for their son.

Lanza described Adam’s behavior as a child as “weird” but never dangerous.

“In preschool and at Sandy Hook, where he was a pupil till the beginning of sixth grade, he sometimes smelled things that weren’t there and washed his hands excessively,” Solomon writes. “A doctor diagnosed sensory-integration disorder, and Adam underwent speech therapy and occupational therapy in kindergarten and first grade. Teachers were told to watch for seizures.”

Lanza said he never had any indication that his son might have harbored a problem with his elementary school.

“Adam loved Sandy Hook school,” he said. “He stated, as he was growing older, how much he had liked being a little kid.”

Lanza said that the first official diagnosis they received concerning Adam’s mental health came when he was 13.

The diagnosis was Asperger’s syndrome, a category that the American Psychiatric Association has since subsumed into the broader diagnosis of an autism spectrum disorder. Adam refused to accept that he had the disorder.

When Adam was 14, the Lanzas took him to the Yale Child Study Center for further diagnosis.

“The psychiatrist who assessed Adam, Robert King, recorded that he was a ‘pale, gaunt, awkward young adolescent standing rigidly with downcast gaze and declining to shake hands.’ He also noted that Adam ‘had relatively little spontaneous speech but responded in a flat tone with little inflection and almost mechanical prosody,’” according to the New Yorker article.

King noted the demands that Adam was increasingly placing on his mother.

“He disapproves if mother leans on anything in the house because it is ‘improper,’” Solomon wrote. “He is also intolerant if mother brushes by his chair and objected to her new high heel boots, because they were ‘too loud.’ If mother walks in front of him in the kitchen, he would insist she redo it.”

Experts say there is no evidence that people who have autism spectrum disorders are more likely than any other group to commit violent crimes.

Peter Lanza said that the diagnosis might have kept them from realizing the danger their son posed.

“If he had been a totally normal adolescent and he was well-adjusted and then all of a sudden went into isolation, alarms would go off,” Lanza said. “But let’s keep in mind that you expect Adam to be weird.”

In 2009, the Lanzas divorced. In September 2010, Adam and his father had an argument about his education, and it was the last time the two spoke.

“I was hurt,” Peter Lanza recalled. “I never expected that I would never talk to him again. I thought it was a matter of when.”

In those years Adam grew more isolated. He eventually stopped speaking to his mother, communicating only via email, according to the state investigation.

Lanza said that if his wife was worried for her safety, she never told anyone, as far as he knew.

“She never confided to her sister or best friend about being afraid of him,” Lanza said. “She slept with her bedroom door unlocked, and she kept guns in the house, which she would not have done if she were frightened.”

Lanza, an accountant and a vice president for taxes at a General Electric subsidiary, insisted that no one could have predicted what his son would do. Still, he regrets not pushing harder to remain a part of his life. Now, his son is a constant presence in his thoughts.

“It’s not like I ever go an hour when it doesn’t cross my mind,” he said.