More than a year has passed since the gruesome attack on Sandy Hook Elementary School in Newtown, Connecticut. Now the father of the shooter, Peter Lanza, is speaking publicly for the first time since that day, expressing that he wishes his son, Adam, had never been born.

Sandy Hook Report Released; No Clear Motive Determined in Mass Shooting

"You can't get any more evil. ... How much do I beat up on myself about the fact that he's my son? A lot," he said, according to The New Yorker.

Authorities say that Adam Lanza killed himself before police arrived at the school, taking the lives of 20 first-graders and six educators in the Dec. 2012 massacre. Peter Lanza said he had not seen his son in two years before the attack. Adam Lanza shot and killed his mother, Nancy Lanza, in their home on the morning of the attack.

Peter Lanza says he has realized that "Adam would have killed me in a heartbeat, if he'd had the chance."

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Peter and Nancy Lanza separated in 2001 and divorced in 2009. He last saw Adam in October 2010 and wanted to maintain contact with him. But Nancy Lanza wrote him an email saying Adam didn't want to see him, despite her efforts to reason with him. Several plans to meet with his son fell through. Peter Lanza said he felt frustrated and even considered hiring a private investigator to find out what his son was doing "so I could bump into him." He said he felt that showing up unannounced at his son's home would only make things worse.

Peter Lanza said Adam was 13 when a psychiatrist diagnosed him with Asperger's syndrome, a form of autism not associated with violence. But he believes the syndrome "veiled a contaminant" that wasn't Asperger's.

"I was thinking it could mask schizophrenia," said Peter Lanza, who lives in Fairfield County, Conn., and is vice president for taxes at a General Electric subsidiary, GE Energy Financial Services.

A spokesman for Peter Lanza said Monday that Lanza would not be commenting further.

Peter Lanza told the magazine that his son as a young child was "just a normal little weird kid" who used to spend hours with his father playing with Legos.

But as he grew older, Adam's mental health problems worsened, according to Connecticut State Police documents. A Yale University professor diagnosed Lanza in 2006 with profound autism spectrum disorder, "with rigidity, isolation, and a lack of comprehension of ordinary social interaction and communications," while also displaying symptoms of obsessive-compulsive disorder, the documents show.

Peter Lanza said his and Nancy Lanza's concerns about Adam increased when he began middle school.

"It was crystal clear something was wrong," he said. "The social awkwardness, the uncomfortable anxiety, unable to sleep, stress, unable to concentrate, having a hard time learning, the awkward walk, reduced eye contact. You could see the changes occurring."