Adam and Peter Lanza on a hike when Adam was about ten. As a child, Peter says, Adam was “just a normal little weird kid.”Background photograph from AP / Western Connecticut State University; family photograph courtesy Peter Lanza

In Peter Lanza’s new house, on a secluded private road in Fairfield County, Connecticut, is an attic room overflowing with shipping crates of what he calls “the stuff.” Since the day in December, 2012, when his son Adam killed his own mother, himself, and twenty-six people at Sandy Hook Elementary School, strangers from across the world have sent thousands upon thousands of letters and other keepsakes: prayer shawls, Bibles, Teddy bears, homemade toys; stories with titles such as “My First Christmas in Heaven”; crosses, including one made by prison inmates. People sent candy, too, and when I visited Peter, last fall, he showed me a bag of year-old caramels. He had not wanted to throw away anything that people sent. But he said, “I was wary about eating anything,” and he didn’t let Shelley Lanza—his second wife—eat any of the candy, either. There was no way to be sure it wasn’t poisoned. Downstairs, in Peter’s home office, I spotted a box of family photographs. He used to display them, he told me, but now he couldn’t look at Adam, and it seemed strange to put up photos of his older son, Ryan, without Adam’s. “I’m not dealing with it,” he said. Later, he added, “You can’t mourn for the little boy he once was. You can’t fool yourself.”

Since the shootings, Peter has avoided the press, but in September, as the first anniversary of his son’s rampage approached, he contacted me to say that he was ready to tell his story. We met six times, for interviews lasting as long as seven hours. Shelley, a librarian at the University of Connecticut, usually joined us and made soup or chili or salads for lunch. Sometimes we played with their German shepherd. When Peter speaks, you can still hear a strong trace of rural Massachusetts and southern New Hampshire, where he and his first wife—Nancy, Adam’s mother—grew up. He is an affable man with a poise that often hides his despair. An accountant who is a vice-president for taxes at a General Electric subsidiary, he maintains a nearly fanatical insistence on facts, and nothing annoyed him more in our conversations than speculation—by me, the media, or anyone else. He is not by nature given to self-examination, and often it was Shelley who underlined the emotional ramifications of what he said.

Peter hadn’t seen his son for two years at the time of the Sandy Hook killings, and, even with hindsight, he doesn’t think that the catastrophe could have been predicted. But he constantly thinks about what he could have done differently and wishes he had pushed harder to see Adam. “Any variation on what I did and how my relationship was had to be good, because no outcome could be worse,” he said. Another time, he said, “You can’t get any more evil,” and added, “How much do I beat up on myself about the fact that he’s my son? A lot.”

Depending on whom you ask, there were twenty-six, twenty-seven, or twenty-eight victims in Newtown. It’s twenty-six if you count only those who were murdered at Sandy Hook Elementary School; twenty-seven if you include Nancy Lanza; twenty-eight if you judge Adam’s suicide a loss. There are twenty-six stars on the local firehouse roof. On the anniversary of the shootings, President Obama referred to “six dedicated school workers and twenty beautiful children” who had been killed, and the governor of Connecticut asked churches to ring their bells twenty-six times. Some churches in Newtown had previously commemorated the victims by ringing twenty-eight times, but a popular narrative had taken hold in which Nancy—a gun enthusiast who had taught Adam to shoot—was an accessory to the crime, rather than its victim. Emily Miller, an editor at the Washington Times, wrote, “We can’t blame lax gun-control laws, access to mental health treatment, prescription drugs or video games for Lanza’s terrible killing spree. We can point to a mother who should have been more aware of how sick her son had become and forced treatment.”

Inadequate gun control and poor mental-health care are problems that invariably define the debate after atrocities such as the one at Newtown. But, important as those issues are, our impulse to grasp for reasons comes, arguably, from a more basic need—to make sense of what seems senseless. When the Connecticut state’s attorney issued a report, in December, CNN announced, “Sandy Hook killer Adam Lanza took motive to his grave.” A Times headline ran “CHILLING LOOK AT NEWTOWN KILLER, BUT NOWHY.’ ” Yet no “motive” can mitigate the horror of a bloodbath involving children. Had we found out—which we did not—that Adam had schizophrenia, or had been a pedophile or a victim of childhood abuse, we still wouldn’t know why he acted as he did.

“Water is on sixteen.”

Interview subjects usually have a story they want to tell, but Peter Lanza came to these conversations as much to ask questions as to answer them. It’s strange to live in a state of sustained incomprehension about what has become the most important fact about you. “I want people to be afraid of the fact that this could happen to them,” he said. It took six months after the shootings for a sense of reality to settle on Peter. “But it’s real,” he said. “It doesn’t have to be understood to be real.”

Adam Lanza was never typical. Born in 1992, he didn’t speak until he was three, and he always understood many more words than he could muster. He showed such hypersensitivity to physical touch that tags had to be removed from his clothing. 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. 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.

Still, photos show him looking cheerful. “Adam loved Sandy Hook school,” Peter said. “He stated, as he was growing older, how much he had liked being a little kid.” Adam’s brother, Ryan, four years older and now a tax accountant in New York, used to joke about how close Peter and Adam were. They’d spend hours playing at two Lego tables in the basement, making up stories for the little towns they built. Adam even invented his own board games. “Always thinking differently,” Peter said. “Just a normal little weird kid.”

Even in an age when a child’s every irregularity is attributed to a syndrome, the idea of a “normal weird kid” seems reasonable enough, but there were early signs that Adam had significant problems. He struggled with basic emotions, and received coaching from Nancy, who became a stay-at-home mother after Adam was born. When he had to show feelings in a school play, Nancy wrote to a friend, “Adam has taken it very seriously, even practicing facial expressions in the mirror!” 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. A couple of years later, according to the state’s attorney’s report, a teacher noted “disturbing” violence in his writing and described him as “intelligent but not normal, with anti-social issues.”

Meanwhile, Peter and Nancy’s marriage was starting to unravel. Peter’s own father had been relatively disengaged from his wife and buried himself in work, and Peter didn’t have a strong model for family life. “I’d work ridiculous hours during the week and Nancy would take care of the kids,” he told me. “Then, on the weekends, she’d do errands and I’d spend time with the kids.” Peter frequently took the boys on weekend hiking trips. In 2001, Peter and Nancy separated. Adam was nine; when a psychiatrist later asked him about it, he said that his parents were as irritating to each other as they were to him.

Peter recalled, “The funny part is that the separation didn’t really change things for the kids very much.” He moved to Stamford, nearly an hour from Newtown, but still saw the boys every weekend. When Adam entered middle school, he proudly took Peter to see it. “And talk about talkative: man, that kid, you couldn’t shut him up!” Peter said. In the years that followed, they would talk about politics. Adam was a fan of Ron Paul, and liked to argue economic theory. He became fascinated with guns and with the Second World War, and showed an interest in joining the military. But he never talked about mass murder, and he wasn’t violent at school. He seldom revealed his emotions, but had a sharp sense of humor. When Peter took him to see Bill Cosby live, Adam laughed for an hour straight. He loved reruns of “The Bob Newhart Show” and “Get Smart,” which he would watch with his dad. One Christmas, Adam told his parents that he wanted to use his savings to buy toys for needy children, and Peter took him shopping for them.

When Adam began middle school, Peter and Nancy’s worries increased. The structure of the school day changed; instead of sitting in one classroom, he had to move from room to room, and he found the disruption punishing. Sensory overload affected his ability to concentrate; his mother xeroxed his textbooks in black-and-white, because he found color graphics unbearable. He quit playing the saxophone, stopped climbing trees, avoided eye contact, and developed a stiff, lumbering gait. He said that he hated birthdays and holidays, which he had previously loved; special occasions unsettled his increasingly sclerotic orderliness. He had “episodes,” panic attacks that necessitated his mother’s coming to school; the state’s attorney’s report says that on such occasions Adam “was more likely to be victimized than to act in violence against another.”

“All of our menu items have a tobacco-juice base.”

“It was crystal clear something was wrong,” Peter 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.” It is hard to be sure whether new problems were setting in or old ones were becoming more apparent. Michael Stone, a psychiatrist who studies mass murder, said that, as children grow up and tasks become more difficult, what seems like a minor impairment becomes major. “They’re a little weird in school. They don’t have friends. They do not get picked for the baseball team,” he said. “But, as they get to the age when kids begin to date and find partners, they can’t. So the sense of deficit, which was minor in grade school, and getting to be a little bit more in junior high, now becomes very acute.” He added that, without the brain getting worse, “life challenges nudge them in the direction of being sicker.”

All the symptoms that afflicted Adam are signs of autism that might be exacerbated by the hormonal shifts of adolescence. When Adam was thirteen, Peter and Nancy took him to Paul J. Fox, a psychiatrist, who gave a diagnosis of Asperger’s syndrome (a category that the American Psychiatric Association has since subsumed into the broader diagnosis of autism spectrum disorder). Peter and Nancy finally knew what they were up against. “It was communicated as ‘Adam, this is good news. This is why you feel this way, and now we can do something about it,’ ” Peter recalled. But Adam would not accept the diagnosis.

Peter and Nancy, who remained amicable in dealing with their children’s needs, looked into special schools, public and private. Peter went to a meeting of the Global and Regional Asperger Syndrome Partnership (GRASP) to talk to adults on the spectrum and to try to imagine a life for his son. He hoped that “eventually we could get him into GRASP and he would form relationships and maybe get married to somebody else with Asperger’s.” Nancy considered moving to a town fifty miles away, where the school system had strong programs for children with special needs, but concluded that the disruption involved would cancel out any benefits. She briefly enrolled Adam in a Catholic school that seemed to offer more structure, but that didn’t go well, either. Fox recommended homeschooling, arguing that the disadvantages of sending Adam to a regular school were worse than those of isolating him from his peers. From eighth grade on, Nancy taught Adam the humanities and Peter met with Adam twice a week to handle the sciences.

Nancy coördinated the home curriculum with Newtown High School to insure that Adam could graduate rather than simply get a G.E.D. She initiated all such major decisions. “I took the back seat,” Peter said. Even after beginning homeschooling, Adam continued to attend Newtown High’s Tech Club meetings. “He fit in there,” Peter said. “They’re all weird and smart.” Adam once held a Tech Club party at home; Nancy wrote to Peter, “It was nice to hear Adam talking to the other kids and everyone joking with him and treating him so well.” But he didn’t understand popularity, and once asked Peter, “Why do you need friends?”

Adam displayed what his father described as “the arrogance that Aspies can have.” He wrote that he was “not satisfied if information related to me is not profound enough. I could not learn anything from the ninth grade history textbook because it did not explain events to a sufficient extent and did not analyze the implementations of the events.” He went on to discount his parents’ teaching, asserting that he had taught himself chemistry.

When Adam was fourteen, shortly after Ryan had left for college, Peter and Nancy took him to Yale’s 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.” Many people with autism speak in a flat tone, and avoiding eye contact is common, too, because trying to interpret sounds and faces at the same time is overwhelming. Open-ended questions can also be intolerable to people with autism, and, when King asked Adam to make three wishes, he wished “that whatever was granting the wishes would not exist.

King noted evidence of obsessive-compulsive disorder, which often accompanies autism. Adam refused to touch metal objects such as doorknobs and didn’t like his mother to touch them, either, because he feared contamination. “Adam imposes many strictures, which are increasingly onerous for mother,” King wrote. “He disapproves if mother leans on anything in the house because it is ‘improper.’ . . . 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.” King was concerned that Adam’s parents seemed to worry primarily about his schooling, and said that it was more urgent to address “how to accommodate Adam’s severe social disabilities in a way that would permit him to be around peers.” King saw “significant risk to Adam in creating, even with the best of intentions, a prosthetic environment which spares him having to encounter other students or to work to overcome his social difficulties.” And he concluded that Nancy was “almost becoming a prisoner in her own house.”

“I can’t decide whether to nap right now or in ten minutes.”

Kathleen Koenig, a nurse specialist in psychiatry at Yale, gave some follow-up treatment. While seeing her, Adam tried Lexapro, which Fox had prescribed. Nancy reported, “On the third morning he complained of dizziness. By that afternoon he was disoriented, his speech was disjointed, he couldn’t even figure out how to open his cereal box. He was sweating profusely . . . it was actually dripping off his hands. He said he couldn’t think. . . . He was practically vegetative.” Later the same day, she wrote, “He did nothing but sit in his dark room staring at nothing.” Adam stopped taking Lexapro and never took psychotropics again, which worried Koenig. She wrote, “While Adam likes to believe that he’s completely logical, in fact, he’s not at all, and I’ve called him on it.” She said he had a biological disorder and needed medication. “I told him he’s living in a box right now, and the box will only get smaller over time if he doesn’t get some treatment.”

Paul Appelbaum, a forensic psychiatrist at Columbia, points out that many young men are asocial and unhappy, spend too much time online, become video-game addicts—but cause no harm. The few dangerous ones are impossible to identify. “Even if we knew who they were or were likely to be, whether they’d actually accept treatment is an open question. Among the hardest people to engage in treatment are young males who may be angry, suspicious, and socially isolated. Coming to a therapist’s office for an hour a week just to pour their heart out doesn’t seem like a particularly attractive opportunity, in general.”

“Adam was not open to therapy,” Peter told me. “He did not want to talk about problems and didn’t even admit he had Asperger’s.” Peter and Nancy were confident enough in the Asperger’s diagnosis that they didn’t look for other explanations for Adam’s behavior. In that sense, Asperger’s may have distracted them from whatever else was amiss. “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,” Peter told me. “But let’s keep in mind that you expect Adam to be weird.” Still, Peter and Nancy sought professional support repeatedly, and none of the doctors they saw detected troubling violence in Adam’s disposition. According to the state’s attorney’s report, “Those mental health professionals who saw him did not see anything that would have predicted his future behavior.” Peter said, “Here we are near New York, one of the best locations for mental-health care, and nobody saw this.”

Peter gets annoyed when people speculate that Asperger’s was the cause of Adam’s rampage. “Asperger’s makes people unusual, but it doesn’t make people like this,” he said, and expressed the view that the condition “veiled a contaminant” that was not Asperger’s: “I was thinking it could mask schizophrenia.” Violence by autistic people is more commonly reactive than planned—triggered, for example, by an invasion of personal space. Studies of people with autism who have committed crimes suggest that at least half also suffer from an additional condition—from psychosis, in about twenty-five per cent of cases. Some researchers believe that a marked increase in the intensity of an autistic person’s preoccupations can be a warning sign, especially if those preoccupations have a sinister aspect. Forensic records of Adam’s online activity show that, in his late teens, he developed a preoccupation with mass murder. But there was never a warning sign; his obsession was discussed only pseudonymously with others online.

Both autism and psychopathy entail a lack of empathy. Psychologists, though, distinguish between the “cognitive empathy” deficits of autism (difficulty understanding what emotions are, trouble interpreting other people’s nonverbal signs) and the “emotional empathy” deficits of psychopathy (lack of concern about hurting other people, an inability to share their feelings). The subgroup of people with neither kind of empathy appears to be small, but such people may act out their malice in ways that can feel both guileless and brutal.

Autism is increasingly invoked in courtrooms as an argument for leniency, sometimes on the ground that the autistic person is confused about cause and effect—a befuddlement defense, as it were. Adam Lanza, however, clearly understood what he was doing. He destroyed one of his hard drives, and left behind an electronic spreadsheet on mass murder, and photographs of himself with a gun to his head. A recent study suggests that a lack of empathy may be connected to insensitivity to physical pain. Despite Adam’s hypersensitivity to more minor irritants, this seems to have been one of his symptoms; his mother warned the school that he might not stop doing something because it hurt.

When I visited Peter, he produced four binders of printouts of his e-mails with Nancy and Adam since 2007. By 2008, when Adam turned sixteen and was going to school only for occasional events, Nancy’s e-mails describe his escalating misery. “He had a horrible night. . . . He cried in the bathroom for 45 minutes and missed his first class.” Two weeks later, she wrote, “I am hoping that he pulls together in time for school this afternoon, but it is doubtful. He has been sitting with his head to one side for over an hour doing nothing.” Later that year: “Adam had a rough night. He moved EVERYTHING out of his room last night. He only kept his bed and wardrobe cabinet.”

“I can see from your résumé that you’re a man.”

In the period that followed the decision to homeschool Adam, Nancy regularly asked Peter not to come when Adam was having a “bad day,” but her correspondence shows no sense of crisis commensurate with the Yale assessment. Peter had begun to feel distanced by the intensity of Adam’s relationship with Nancy, although he did not feel that the intensity was “by its nature problematic.” His approach to parenting was as docile as Nancy’s was obsessive. She indulged Adam’s compulsions. “She would build the world around him and cushion it,” Peter said. Adam had difficulties with coördination and, when he was seventeen, Peter told Nancy that he had had to pause to retie his shoes on a hike. Nancy responded in astonishment, “He tied his own shoes?”

Adam’s sense of humor endured. When he was sixteen, he found a picture of Karl Marx (huge beard), Lenin (small beard), Stalin (mustache), and Mao (clean-shaven), and sent it around with a caption, “Comrades, we must rectify the faltering facial hair standards.” Peter thought it was hilarious and got T-shirts made with the image and Adam’s words. Everyone tried to encourage Adam and looked for ways to engage with him. Nancy would take him on trips to the shooting range. Nancy and Peter thought that their son was nonviolent; the best way to build a connection to someone with Asperger’s is often to participate in his fascinations.

All parenting involves choosing between the day (why have another argument at dinner?) and the years (the child must learn to eat vegetables). Nancy’s error seems to have been that she always focussed on the day, in a ceaseless quest to keep peace in the home she shared with the hypersensitive, controlling, increasingly hostile stranger who was her son. She thought that she could keep the years at bay by making each day as good as possible, but her willingness to indulge his isolation may well have exacerbated the problems it was intended to ameliorate.

In the fall of 2009, the Lanzas finally divorced. One provision of the divorce was that Peter buy Adam a car. Peter bought him a Honda Civic and taught him to drive, and he told me that his son was “the most cautious driver on the face of the earth.” Peter never worried about Adam’s breaking rules of any kind. He did feel that Adam was losing interest in him, but the estrangement didn’t strike Peter as ominous; he, too, had become alienated from his parents in late adolescence. “I had to give him space,” Peter explained. “He’ll get more mature; I’ll just keep doing what I can, staying involved.”

During that year, Adam developed his private obsession with killing. He started editing Wikipedia entries on various well-known mass murderers and seems to have been eerily well informed. But although there were still no outward signs of violent tendencies, he was becoming ever harder to deal with. Nancy wrote to Peter that Adam would sometimes close his door when she tried to talk to him.

Schoolwork often triggered a sense of hopelessness. “He was exhausted and lethargic all day, and said he was unable to concentrate and his homework isn’t done,” she wrote. “He is on the verge of tears over not having his journal entries ready to pass in. He said he tried to concentrate and couldn’t and has been wondering why he is ‘such a loser’ and if there is anything he can do about it.” He had been taking classes at Western Connecticut State University—for high-school credit—but he struggled there. “He wouldn’t speak on the way home and had his hood completely covering his face,” Nancy wrote one day. “He went straight to his room and won’t eat. I gave him time alone to compose and have tried to speak to him twice now, but he just keeps saying, ‘It does not matter’ and ‘leave me’ ‘I don’t want to speak of it.’ ” Two months later, Nancy recorded his despair when faced with some coursework in German: “He finally and tearfully said that he can’t complete the German. He can’t understand it. He has spent hours on the worksheets and can’t comprehend them.”

Nancy wanted to take him to a tutor, but, she wrote, “Even ten minutes before we should leave he was getting ready to go, but then had a meltdown and began to cry and couldn’t go. He said things like it’s pointless, and he doesn’t even know what he doesn’t know.” In early 2010, when Nancy told Peter that Adam had been crying hysterically on the bathroom floor, Peter responded with uncharacteristic vehemence: “Adam needs to communicate the source of his sorrow. We have less than three months to help him before he is 18. I am convinced that when he turns 18 he will either try to enlist or just leave the house to become homeless.” Nancy replied, “I just spent 2 hours sitting outside his door, talking to him about why he is so upset. He failed every single test during that class, yet he thought he knew the material.” Later that day, she wrote, “I have the feeling when he said he would rather be homeless than to take any more tests, he really meant it.” Nancy said that Adam had been pretending to go to classes and passing his time in the library.

“Who do we talk to about buying your planet?”

Adam always had aspirations beyond his abilities. His list of colleges started with Cornell, for which he clearly didn’t have the academic record. Then he announced that he was going to enlist in the military when he turned eighteen, in April, 2010; he wanted to join the Army Rangers, an élite regiment. “What do you do?” Peter wondered. “You tell him, ‘Adam, that’s unrealistic’?” When the time came, Adam didn’t sign up. Peter took Adam to visit Norwich University, which has a military program, but they concluded that Adam should take classes at Norwalk Community College, near Stamford, before attempting campus life anywhere. Adam wanted to take five classes, but Peter said it was more than he could cope with, and suggested two classes that they could work on together. Peter went to pick him up for a weekend visit, and Adam refused to go. Peter said, “Adam, we’ve got to figure out a system so I can work with you.” Adam was angry. “I hardly ever saw him pissed, but he was pissed,” Peter recalled. “And it was, like, ‘I’m taking the five classes. I’m taking them.’ ” It was September, 2010: the last time Peter saw his son.

Earlier that year, Nancy had written, “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.” An e-mail that Adam sent Peter to get out of another meeting sounded innocuous—“I apologize for not wanting to go today. I have not been feeling well for the last couple of days”—but Nancy’s updates painted a more fraught picture. “He is despondent and crying a lot and just can’t continue. . . . I have been trying to get him to see you and he refuses and every time I’ve brought the subject up it just makes him worse,” she wrote. Nancy surmised that Adam resented Peter’s warning about the heavy course load.

Peter was frustrated but felt that he couldn’t show up at the house in Newtown to force an encounter. “It would have been a fight, the last thing I’d want to be doing. Jesus. . . . If I had gone there unannounced and just, ‘I want to see Adam.’ ‘Why are you doing this?’ Adam would be all bent about me.” Later, Peter remarked, “If I said I’m coming, she’d say, ‘No, there’s no reason for that.’ I mean, she controlled the situation.” Peter tried to remain conciliatory, and never introduced Adam to Shelley, suspecting that it would be more than he could handle. (He did introduce her to Ryan, who had moved to New Jersey after graduating college.) He considered hiring a private investigator “to try to figure out where he was going, so I could bump into him.” If he had, he might have discovered that Adam went regularly to a local movie house to play a game called Dance Dance Revolution, spending up to ten hours at a stretch listening to music and trying to keep up with complex dance moves on an illuminated platform. He was still doing so a month before the shootings.

I wondered how Peter had felt through this period. “Sad,” he said. “I was hurt. I never expected that I would never talk to him again. I thought it was a matter of when.” He asked, “How much do you accommodate the demands and how much do you not? Nancy tended to, as did I.” Peter added, “But I think he saw that he could control her more than he could control me.” Adam had also cut off communication with Ryan, whom he last saw two Christmases before the shootings. According to Peter, Ryan reached out several times, but Adam never responded. Peter and Shelley now suspect that Adam deliberately shut them out to hide his psychological decay. Peter said, “I didn’t understand that Adam was drifting away.”

By 2011, Nancy’s messages had grown terse. Peter attributed this to his remarriage rather than to a change in Adam’s condition. That October, a little more than a year before the shootings, she related that Adam “has been doing very well and has become quite independent over the last year. He is starting to talk about going back to school which would be nice.” But the state’s attorney’s report notes that people who worked on the property couldn’t enter the house and were warned never even to ring the doorbell.

In early 2012, Nancy said that Adam had agreed to see Peter in the spring, but nothing came of it. Nine months later, Peter protested that Adam never even acknowledged his e-mails. Nancy wrote, “I will talk to him about that but I don’t want to harass him. He has had a bad summer and actually stopped going out.” She said that his car had sat unused for so long that its battery was dead. She played down the significance of Adam’s failure to answer his father’s e-mails: “He stopped emailing me a year ago or so, but I assumed it was because he actually started talking to me more.” However, the state’s attorney’s report suggests that Nancy’s account was misleading: Adam had stopped speaking to his mother and communicated only through e-mail. “It bothers me that she was telling me he doesn’t use e-mail at the same time she was e-mailing him,” Peter told me. He thinks Nancy’s pride prevented her from asking for help. “She wanted everyone to think everything was O.K.”

As Adam’s isolation deepened, Nancy’s naïveté began to blur into denial. She started making plans to move with Adam, possibly to Seattle, although she didn’t mention those plans to Peter. She had also suggested to a friend that she’d be living with Adam for a “very long time,” a situation that could have been upsetting for a young man too set on independence to let his father help him with his coursework. Nancy’s mixture of hovering appeasement and disregard for professional help now seems bewildering. Yet similar choices have worked well for others: some people with autism respond best to a mixture of laissez-faire and active indulgence.

“Watch out for his right hook.”

Peter’s final communication from Nancy, the month before the shootings, was about buying Adam a new computer. Peter wanted to give it to Adam personally. Nancy said she’d discuss it with Adam after Thanksgiving. “I was doing everything I could,” Peter said. “She was doing way more. I just feel sad for her.” Peter is convinced that Nancy had no idea how dangerous their son had become. “She never confided to her sister or best friend about being afraid of him. She slept with her bedroom door unlocked, and she kept guns in the house, which she would not have done if she were frightened.” About a week before the shootings, Nancy reportedly told an acquaintance, “I’m worried I’m losing him.” But losing him seemed to be a matter of his withdrawal, not of violence. The cautiousness with which Nancy responded to her son’s demands indicates anxiety rather than fear, and it must have made her as lonely as it did him.

Matricide is usually committed by overprotected boys—by a son who wishes, as one study puts it, “with his desperate act, to free himself from his state of dependency on her, a dependency that he believes has not allowed him to grow up.” Another study proposes that, in each case examined, “the mother-child relationship became unusually intense and conflict-laden,” while the fathers “were uniformly passive and remained relatively uninvolved.” The state’s attorney’s report says that when Nancy asked Adam whether he would feel sad if anything happened to her, he replied, “No.” A Word document called “Selfish,” which was found on Adam’s computer, gives an explanation of why females are inherently selfish, written while one of them was accommodating him in every possible way.

Peter does not think that Adam had any affection for him, either, by that point. He said, “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.”

On the morning of December 14, 2012, Peter went to get lunch at work and found colleagues clustered around a television. 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.”

As soon as she got home, they called Ryan and began the two-hour drive to his place, in Hoboken. Ryan had also left his office early; by the time he got home, the police had taped off his apartment building. Adam had been carrying Ryan’s I.D., which had led to the confusion. Ryan approached the police with his arms up and said, “You’re looking for me, but I didn’t do it.” He was taken to a police station, so Peter and Shelley headed there, too. They were questioned for a couple of hours and were made to wait for two more before they were allowed to see Ryan. They went to the home of an aunt of Peter’s to regroup; they were shuttled to a hotel, then to Shelley’s family’s house and other safe houses, with a canine unit supplied by the police for security; they were interviewed by the F.B.I., the state police, and various local authorities. “We didn’t even have clothes,” Peter said. “I had to borrow my lawyer’s pants.” Eventually, they headed to New Hampshire to arrange Nancy’s funeral, and had to evade a stakeout by news media, which wanted to cover it. I asked what they had done about a funeral for Adam. “No one knows that,” Peter said. “And no one ever will.”

Adam Lanza was a terrorist for an unknowable cause who committed three distinct atrocities: he killed his mother; he killed himself; he killed children and adults he’d never met before. Two of these acts are explicable; the third, incomprehensible. There are many crimes from which most people desist because we know right from wrong and are careful of the law. Most people would like to have things that belong to others; many people have felt murderous rage. But the reason that almost no one shoots twenty random children isn’t self-restraint; it’s that there is no level at which the idea is attractive. Since 2006, according to a USA Today study, there have been two hundred and thirty-two mass killings—meaning, more than four deaths apiece, not including the killer—in the United States. But fewer than fifteen per cent involved random, unknown victims.

“You eat dog—excellent!”

The problem with generalities about mass murderers is that the sample size is tiny, and most die before they can be examined. Almost half of all mass murderers commit suicide in the act, and many others are killed by police. Indeed, Paul Appelbaum, the forensic psychiatrist at Columbia, views such cases as “suicides with murder as an epiphenomenon, rather than murders that happen to end in suicide.” The opposite view is equally possible: Henry J. Friedman, a psychiatry professor at Harvard, has said that for these killers murderousness is “a primary rather than a reactive state,” and that their “desire to end life early surrounded by an aurora of apocalyptic destruction” does not signal the “true depressive despair” typical of suicides. But, for Adam, killing others and suicide were both crucial. The link seems clear: the more Adam hated himself, the more he hated everyone else. Émile Durkheim, the great scholar of suicide, wrote that it can be “not an act of despair, but of abnegation.” Adam abnegated humanity with his act.

Scientists are sequencing Adam’s DNA to see if they can find anomalies that might explain what was broken in him. And yet, if someone has committed heinous crimes and is then found to have bad genes or a neurological abnormality, should we presume that biology compelled him? It’s a circular argument that conflates what describes a phenomenon and what causes it. Everything in our minds is encoded in neural architecture, and if scanning technologies advance far enough we’ll see physiological evidence of a college education, a failed love affair, religious faith. Will such knowledge also bring deeper understanding?

Legal definitions of insanity still focus on psychosis, the delusions of which are held to diminish responsibility. Medical conceptions include many additional bizarre behaviors, thoughts, and feelings. The legal definition has historically encompassed both questions of agency (he didn’t know what he was doing) and morality (he didn’t know that what he was doing was wrong). The psychiatric profession doesn’t consider mass killers to be necessarily insane, which distresses Peter. For him, the crime defines the illness—as he said, soon after we met, you’d have to be crazy to do such a thing. He found the idea of Adam’s not being insane much more devastating than the thought of his being insane. Peter has searched the psychiatric literature on mass killers, trying to understand what happened to his son. He came across the work of Park Dietz, a psychiatrist who, in 1986, coined the term “pseudocommando.” Dietz says that for pseudocommandos a preoccupation with weapons and war regalia makes up for a sense of impotence and failure. He wrote that we insist that mass killers are insane only to reassure ourselves that normal people are incapable of such evil.

Crimes of passion are relational, whereas plotted crimes such as Adam’s are unsocial. But the dichotomy isn’t clear-cut; most crimes lie along a spectrum. So Sandy Hook was a culmination—neither sudden nor entirely calculated, at least until the very end. James Knoll, a forensic psychiatrist at SUNY, has written that Adam’s act conveyed a message: “I carry profound hurt—I’ll go ballistic and transfer it onto you.” That’s as much motive as we’re likely to find.

On the anniversary of the massacre, Peter and Shelley finally went through “the stuff,” reading letters of support they previously hadn’t felt able to face. Peter wanted the writers to know how much their words helped him. “There was a woman whose brother shot up a church,” Peter said. “Killed a bunch of people and himself. Saying how sorry she is. There was a woman whose husband stabbed and killed a child. People having Masses said for Adam.” Some included phone numbers and said to call if he needed anything. Other letters were peculiar: one suggested that Adam had been drugged by the C.I.A. and forced to his acts in order to foment support for gun-control legislation. The anniversary itself felt insignificant. “It’s not like I ever go an hour when it doesn’t cross my mind,” Peter said when we met that day.

Peter has offered to meet with the victims’ families, and two have taken up his offer. “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.” The only reason Peter was talking to anyone, including me, was to share information that might help the families or prevent another such event. “I need to get some good from this. And there’s no place else to find any good. If I could generate something to help them, it doesn’t replace, it doesn’t—” He struggled to find the words. “But I would trade places with them in a heartbeat if that could help.”

Peter told me, “I get very defensive with my name. I do not like to even say it. I thought about changing it, but I feel like that would be distancing myself and I cannot distance myself. I don’t let it define me, but I felt like changing the name is sort of pretending it didn’t happen and that’s not right.” But Peter has found the visibility hard. Old friends have been unflagging in their support, but Peter said he thought that he might never make new friends again. “This defines who I am and I can’t stand that, but you have to accept it.”

“And in this corner, weighing five pounds more than she’d like . . .”

The last time I saw Peter, he had taken out a picture of himself at the beach with his two sons. “One thing that struck me about that picture is that it’s clear that he’s loved,” he said. Peter has dreamed about Adam every night since the event, dreams of pervasive sadness rather than fear; he had told me that he could not be afraid of his fate as Adam’s father, even of being murdered by his son. Recently, though, he had had the worst nightmare of his life. He was walking past a door; a figure in the door began shaking it violently. Peter could sense hatred, anger, “the worst possible evilness,” and he could see upraised hands. He realized it was Adam. “What surprised me is that I was scared as shit,” he recounted. “I couldn’t understand what was happening to me. And then I realized that I was experiencing it from the perspective of his victims.”

I wondered how Peter would feel if he could see his son again. “Quite honestly, I think that I wouldn’t recognize the person I saw,” he said. “All I could picture is there’d be nothing there, there’d be nothing. Almost, like, ‘Who are you, stranger?’ ” Peter declared that he wished Adam had never been born, that there could be no remembering who he was outside of who he became. “That didn’t come right away. 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.” ♦