(NBC NEWS) -- Speaking publicly for the first time, the father of the Newtown, Conn., school killer says he wishes his son had never been born.
In one of a series of interviews with The New Yorker that began in September, Peter Lanza says this of his son Adam, 20, who killed his mother, Nancy, before gunning down 20 pupils, six staff members and himself at Sandy Hook Elementary School in December 2012:
"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."
Lanza, a vice president for GE Energy Financial Services, was divorced from Adam's mother since 2009 and hadn't seen his son for more than two years at the time of the killings, he told the magazine for a 7,600-word story published Monday.
New Yorker writer Andrew Solomon said Lanza approached him in September because, he quoted Lanza as saying, "I want people to be afraid of the fact that this could happen to them."
"With hindsight, I know Adam would have killed me in a heartbeat, if he'd had the chance," Lanza said. "I don't question that for a minute. The reason he shot Nancy four times was one for each of us: one for Nancy; one for him; one for [his brother] Ryan; one for me."
Lanza says that by the time his son entered middle school, "it was crystal clear something was wrong." Adam was socially awkward, anxious, unable to concentrate andafflicted with insomnia.
The family thought they'd gotten an answer when Adam was diagnosed with Asperger's syndrome, a high-functioning form of autism, at age 13. But after a severe reaction to the anti-anxiety drug escitalopram, he refused to take any psychotropic drugs thereafter - behavior that profoundly concerned a psychiatric specialist who treated him.
"While Adam likes to believe that he's completely logical, in fact, he's not at all," the specialist wrote in an assessment.
Still, Peter Lanza says he is convinced the Asperger's diagnosis had little to do with the mass killings. Instead, he said Asperger's may have been masking schizophrenia.
"Asperger's makes people unusual, but it doesn't make people like this," he told the magazine.
Meawhile, Lanza refuses to talk about a lingering mystery: where or how his son's body was disposed of.
"No one knows that," he says. "And no one ever will."