In a harrowing interview with the New Yorker, the first since his son, Adam, shot and killed 20 students and six teachers in December 2012 at Sandy Hook Elementary, Peter Lanza described the horror, guilt, and regret he's felt since the tragedy. "Any variation on what I did and how my relationship was [with Adam] had to be good, because no outcome could be worse," Lanza said. "You can't get any more evil."

Despite an early diagnosis of sensory-integration disorder, Lanza told Andrew Solomon that Adam was "just a normal, weird little kid" who was "always thinking differently." Lanza and Adam's mother, Nancy, separated when Adam was nine, but it wasn't until fifth grade that his problems became more obvious.

From the New Yorker:

According to the state's attorney's report, when Adam was in fifth grade he said that he "did not think highly of himself and believed that everyone else in the world deserved more than he did." That year, Adam and another boy wrote a story called "The Big Book of Granny," in which an old woman with a gun in her cane kills wantonly. In the third chapter, Granny and her son want to taxidermy a boy for their mantelpiece. In another chapter, a character called Dora the Berserker says, "I like hurting people. . . . Especially children." Adam tried to sell copies of the book at school and got in trouble.

"It was crystal clear something was wrong," Lanza 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."

Adam was diagnosed with Asperger's syndrome at age 13; by eighth grade, he was being homeschooled by his mother, Nancy. "Why do you need friends?" Lanza remembers Adam asking after he met with the tech club at Newtown High School a few years later.

In September 2010, Lanza saw his son for the last time. "He does not want to see you. I have been trying to reason with him to no avail. I don't know what to do," Nancy wrote in an email.

"I was hurt," Lanza told Solomon. "I never expected that I would never talk to him again. I thought it was a matter of when."

When news of the shooting broke, Lanza was at work. From the New Yorker:

Shocked by the developing news, Peter said, "Both my kids went to that school," and went back to his office. Then news reports mentioned that a twenty- and a twenty-four-year-old were involved (the ages of his two sons) and that the shooter had attended the school. Unable to get any work done, he drove home to watch the coverage. A reporter was waiting in his driveway, and told him that somebody at his house was involved in the shootings. Peter closed the door, turned on the TV, and saw that CNN was identifying Ryan as the shooter. But he knew better, and called Shelley at work. She told me, "Peter said, 'It's Peter. I think it's Adam.' I didn't recognize his voice. And he just said it again: 'It's Peter, it's Peter, it's Adam.' And I still didn't understand him. And he said, 'I think it's Adam, it's Adam.' When it hit me, I screamed and started shaking violently."

Eventually, Lanza realized Adam would've killed him, too. "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. 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."

Now, Lanza says, he wishes Adam had never been born.

"That didn't come right away," he told Solomon. "That's not a natural thing, when you're thinking about your kid. But, God, there's no question. There can only be one conclusion, when you finally get there. That's fairly recent, too, but that's totally where I am."

In the past year, he's met with the families of two of Adam's victims. "It's gut-wrenching," he said. "A victim's family member told me that they forgave Adam after we spent three hours talking. I didn't even know how to respond. A person that lost their son, their only son."

[Image via Getty]