Adam Lanza was fascinated with chimpanzees because of their capacity for empathy, but could show little or none himself.
He could write stories that struck horror into a teacher's heart, then turn around and craft a poem so beautiful it moved listeners to tears.
As a kid growing up in Connecticut, he rode bikes, played baseball and saxophone, and kept hamsters. As a man, he taped black garbage bags over his bedroom windows, retreating into a world of violent video games, guns and statistics on mass murder.
Despite the release Friday by Connecticut state police of thousands of pages of interviews, photographs and writings, the man who gunned down 20 first-graders and six adults at Newtown's Sandy Hook Elementary School on Dec. 14, 2012, remains an enigma.
Some of the most tantalizing evidence of the inner workings of the 20-year-old Newtown man's brain appears to be contained in writings that the police chose not to release.
An eight-page document titled simply, "me," is described in a police inventory as "detailing relationships, ideal companion, culture, voting, personal beliefs, describes doctors touching children as rape." Another, named "tomorrow," apparently contains details about the author's "desires, list of the benefits of being thin and negative connotations associated with being overweight, list of goals ..."
What the files do show is a deeply troubled young man, living with a single mother who was either unable or unwilling to accept the depths of his illness.
The picture most people have of Adam Lanza is the skeletal, blank face from photographs released by police following the massacre. Childhood photos show a smiling boy who could look into a camera, but signs of trouble — if not violence — emerged early.
In his preteen years, Lanza had difficulty with speech and was "being followed medically for seizure activities," according to investigators.
"In preschool his conduct included repetitive behaviors, temper tantrums, smelling things that were not there, excessive hand washing and eating idiosyncrasies," prosecutors said in one report.
But Lanza's real problems appear to have begun after his parents' separation in 2001, when he was 9 years old.
Adam had attended Sandy Hook Elementary. In fifth grade, he turned in a cute story about a "chicken tree" whose hen fruit "contains everything you ever will need to live like calcium and water."
"It spits out seeds every four hours by using its long chute," he wrote in a slanted, choppy block script. "The vines that holds the chicken is very soft and very strong."
That same year, Lanza produced a more disturbing work.
According to a boy who worked on it with him in class, "The Big Book of Granny" was supposed to be a "comic-style book" in the vein of "Calvin & Hobbes." It was far from it.
In a section of the book labeled "Granny's Clubhouse of Happy Children," typed as dialogue from an imaginary television show, Granny and her son, "Bobolicious," terrorize a group of children. In one episode, Bobolicious tells the children they're going to play a game of "Hide and go die."
Granny uses her "rifle cane" to kill people at a bank, hockey game and Marine boot camp. She also goes back in time and murders the four Beatles, according to a police synopsis.
The book also contains several chapters with the adventures of "Dora the Beserker" and her monkey, "Shoes" — a clear knockoff of the popular children's show "Dora the Explorer."
When Granny asks Dora to assassinate a soldier, she replies: "I like hurting people ... Especially children." In the same episode, Dora sends "Swiper the Raccoon" into a day care center to distract the children, then enters and says, "Let's hurt children."
In the real kids' show, Dora has a backpack that contains a talking map. In Lanza's perversion, the group carries a bag stuffed with an AK-47, an M-16, a shotgun, a musket and a rocket launcher.
The boy who drew the cover illustration — showing Granny firing her cane gun — thought the book was turned in, but that remains unclear.
He told investigators that Lanza was "weird" and "would sit by himself on the other side of the room and would not talk or associate with anybody else." Lanza also came to school with a briefcase, he recalled.
One undated poem contained in the police files is titled, "No frogs, No kids":
"Too many ants are coming.
Ants over populate.
Ants dig dirt.
dirt grows plants.
Bees come to plants.
Cock Robin died.
ants feed bees to babies.
Ants will overtake to win.
One baby died.
3 eggs won't hatch.
one bird has no voice."
By seventh grade, a teacher told investigators, Lanza's writing was "so graphic that it could not be shared" — except with the principal. The teacher said Adam's parents were not "upfront" about his mental abilities.
Adam would write essays "obsessing about battles, destruction and war," said the teacher, whose name and gender were redacted. "In all my years of experience, I have known ... boys to talk about things like this but Adam's level of violence was disturbing."
But when the teacher asked Adam to submit something else to share with the class, he produced a lovely poem.
"Adam shared his poem in public with his father present, who was in tears," the teacher told police.
Peter Lanza has declined to speak publicly about his son. But in interviews with investigators, he said that his son's life appeared to take a turn after his 11th birthday.
He seemed "less happy, stressed and frustrated," his father said, but he never exhibited any "outward signs of anger or aggression." He told people he "did not think highly of himself and believed that everyone else in the world deserved more than he did," according to investigators.
Dr. Robert A. King, a professor at the Yale School of Medicine Child Study Center, conducted a three-hour psychiatric evaluation of Lanza in October 2006. King diagnosed Lanza with "profound Autism Spectrum Disorder, with rigidity, isolation, and a lack of comprehension of ordinary social interaction and communications."
Peter Lanza, who was estranged from his son, told police that his son had Asperger's syndrome, a type of autism that is not associated with violence.
King said Lanza also displayed symptoms of obsessive-compulsive disorder. The boy would change his socks 20 times a day and sometimes would go through a box of tissues in 24 hours because he couldn't bear to touch a doorknob with his bare hand.
Kathleen Koenig, an advanced practice nurse at the Yale Child Study Center who conducted four face-to-face interviews with Adam Lanza in 2006 and 2007, described him as "emotionally paralyzed."
Koenig said she prescribed him with an antidepressant/anti-anxiety medication. She said the mother's response to her recommendations for Lanza as "non-compliant."
After prescribing Lanza a "small dose" of the drug, the nurse said, she received a call from Nancy reporting that he was "unable to raise his arm." Koenig didn't believe the medication could cause such a side effect, but Nancy Lanza did and discontinued the treatment.
When Adam missed an appointment, Koenig said, his mother "failed to schedule" any follow-up visits.
His freshman year at Newtown High School, Lanza's mother withdrew him because of "stresses over papers, classes, pressure from grades and dealing with his disease," an acquaintance told police. But that same person told authorities that Lanza "never completely accepted that he had a disease."
Peter Lanza told the investigators that his ex-wife decided to home school Adam, because he seemed more comfortable that way. But while their 2009 divorce file shows an amicable split, there are some suggestions in the newly released documents that the couple had differences over how Adam was being raised.
In a February 2007 email to a doctor, Nancy Lanza wrote: "I have been more concerned with keeping him as comfortable as possible and just getting through each day." His father, on the other hand, was focused on "stabilization."
Peter Lanza told police his and Adam's relationship "deteriorated" in late 2010, and that his son eventually stopped responding even to emails. Adam's older brother, Ryan, hadn't had any contact with him since 2010.
Back at Newtown High, Adam was a member of the Tech Club — although he did not engage much with the others. Instead of participating in gym class, he was allowed to keep a journal.
At 6 feet tall, Adam weighed just 112 pounds. Witnesses told investigators that Adam was a vegan and drank water "with a certain amount of salt added to it."
One person told police that Lanza never used drugs or alcohol and "hated the thought of it."
Despite all the evidence that he was a loner, Lanza had not yet cut himself off completely.
In recent years, Lanza would spend nearly every weekend playing the videogame Dance Dance Revolution at a nearby movie theater. In fact, he was there so often and long, people there called him "DDR guy."
Someone who befriended him there told authorities that Lanza was not completely withdrawn.
"Emotion wasn't something expressed in particularly verbose or grandiose fashion but it was expressed," the unnamed witness, who met Lanza sometime in 2011, told investigators in a lengthy email. "He was capable of laughing, smiling and making jokes though always in a dry fashion."
The two had wide-ranging conversations.
They discussed chimp society, with Lanza remarking that chimps "were able to show more empathy to members of their group than humans were at time." Lanza said humans were "glorified animals" with a "flawed faculty of judgment."
Adam was interested in Japanese techno music and had taken Chinese lessons with a private tutor. He even talked about joining the military.
In general, the friend said, Lanza would adopt "a very nihilist take on things" and seemed "overtly fatalistic and bleak." Lanza would disappear for weeks at a time, after which he would say he was "having an existential crisis."
He liked to go "off grid" from time to time, and frequently reformatted his computer hard drives, presumably to cover his tracks, the friend said.
Another topic of discussions was pedophilia.
Among the documents investigators found on Lanza's computer was one titled "pbear" that investigators described as "advocating pedophiles' rights and the liberation of children." Another, called "Lovebound," was a screenplay describing a relationship between a 10-year-old boy and a 30-year-old man.
Lanza said his stance on issues of mental illness, including pedophilia, "would cause others to make snap judgments about him as an apologist," Lanza's theater friend told authorities.
Eventually, however, Lanza even fell out with his DDR buddy. In June 2012, the man told authorities, Lanza said "that he should not expect him to participate in any more activities with him."
Workers at the theater say they last saw Lanza there in August or September 2012. His isolation had now become total.
Two weeks before the shootings, the documents say, Nancy Lanza told a lifelong friend that Adam was growing "increasingly despondent" and had refused to leave his room for three months. Despite sleeping on the same floor, they communicated only via email; one document in the police inventory is a "list of problems and requests from the shooter to Nancy."
The only thing they seemed to have in common was a love of guns. Nancy and Adam took a firearms safety course together, and she took him to a range to fire some of the several weapons she kept at home.
But if that was meant to bring them closer, it did not appear to have worked. Nancy Lanza told a friend that she asked her son whether he would feel bad should anything happen to her, and he replied, "No."
But as one person told the FBI: "Nancy was not afraid of Adam, but was afraid for him." Still, she was trying.
Nancy Lanza told a friend she was thinking of selling her home and moving to Washington state or North Carolina, where she had a friend who might be willing to give Adam a computer job. Adam refused to stay in hotels, and his mother talked about buying a camper for him to sleep in.
On Dec. 10, 2012, she decided to try a little "experiment." She was going to make a short trip to New Hampshire to see how Adam fared alone for a few days.
Shortly before noon, she texted a friend that "she had gotten off to a rough start." Adam had "bumped his head" early that morning, and they were "dealing with blood," according to the police files.
Nancy Lanza returned home late in the evening of Dec. 13.
Within 12 hours, she, her son and 26 others were dead.
Contributing to this report were Associated Press writers John Christoffersen in New Haven, Conn.; David Sharp in Portland, Maine; Jack Gillum in Washington; Nancy Albritton in Philadelphia; Frank Eltman in Mineola, N.Y.; David Eggert in Lansing, Mich.; Kantele Franko in Columbus, Ohio; Michelle L. Johnson and Dinesh Ramde in Milwaukee; David Klepper in Providence, R.I.; Amanda Lee Myers in Cincinnati; Bob Salsberg in Boston; Rik Stevens in Concord, N.H.,; Terry Tang in Phoenix; Laura Wides in Miami and Katie Zezima in Newark, N.J.