As with many murder-suicides, the suspect in the Sandy Hook Elementary School shooting took to his grave the reasons that compelled him to kill more than two dozen people before taking his own life in the second deadliest school shooting in U.S. history.
But those who knew the alleged shooter grasped to reconcile the difference between the quiet, withdrawn 20-year-old without a criminal record and the man who donned black fatigues and a military vest and rained hell at the Newtown, Conn., school last week.
Police say the shooter was Adam Lanza, and that he killed his mother, Nancy, in their home before walking into the school and spraying with bullets 26 more people --20 of them children no older than 7.
The rampage ended when Lanza apparently took his own life in a classroom. With him were three firearms: a .223-caliber Bushmaster rifle and two handguns, a Glock and a Sig Sauer.
Connecticut law requires gun owners to be at least 21 years old. The guns, authorities said, belonged to his mother.
Police have yet to disclose a motive for the attack -- which left those who knew Lanza trying to discern whether anything in his past could have foreshadowed the present.
Lanza moved to Connecticut from Kingston, New Hampshire, with his parents and older brother Ryan, according to a booklet for the town's Newtown's Bennetts Farm neighborhood. He enjoyed soccer, skateboarding and video games, the publication said.
In September 2009 -- when Lanza was 17 -- his mother and father divorced, court documents show.
What happened after that for him isn't clear, except that he continued to lived in the picturesque, 300-year-old Connecticut town.
His father, Peter, remarried and lived not far from Newtown, an official said. He was questioned by authorities after the shooting. So, too, was his 24-year-old brother Ryan.
Authorities have offered few details about Lanza. He had no known criminal record, a law enforcement official said.
One of Lanza's aunts, Marsha, described him as a "quiet, nice kid" who had issues with learning, she said. Her husband is Lanza's paternal uncle.
"He was definitely the challenge of the family in that house. Every family has one," she told CNN affiliate WLS. "They have one. I have one. But never in trouble with the law, never in trouble with anything."
She said Lanza's mother "battled" with the school board and ended up having her son home-schooled.
"She had issues with school," said the aunt, who lives in Crystal Lake, Illinois. "I'm not 100% certain if it was behavior or learning disabilities, but he was a very, very bright boy. He was smart."
Alex Israel was in the same class at Newtown High School with Lanza and lived a few houses down from him.
"You could definitely tell he was a genius," Israel told CNN, adding she hadn't talked with him since middle school. "He was really quiet, he kept to himself."
Others in Newtown who knew Lanza said they had no idea he'd ever be responsible for such horror.
His former bus driver, Marsha Moskowitz, told CNN affiliate WABC that he was "a nice kid, very polite" like his brother.
"It's a shock to even know (the family)," she said. "You can't understand what happened."
A relative told investigators that Lanza had a form of autism, according to a law enforcement official, who spoke under condition of anonymity due to the sensitive nature of the investigation.
But a national autism committee cautioned against speculating about a link between autism and violence.
"Autism is not a mental health disorder - it is a neurodevelopmental disorder," said the Autism Research Institute's Autistic Global Initiative Project. "The eyes of the world are on this wrenching tragedy -- with 1 in 88 now diagnosed, misinformation could easily trigger increased prejudice and misunderstanding."
A former classmate told CNN affiliate WCBS that Lanza "was just a kid" -- not a troublemaker.
"I don't know who would do anything like this," the classmate said, before walking away distraught. "This is unspeakable."
The suspect's father was also at a loss for explanation. He sent his condolences to the families of victims in a statement released Saturday.
"Our family is grieving along with all those who have been affected by this enormous tragedy," he said. "No words can truly express how heartbroken we are. We are in a state of disbelief and trying to find whatever answers we can."
In New Hampshire, relatives of Nancy Lanza -- the mother -- released a statement in which they too expressed shock and sadness.
"On behalf of Nancy's mother and siblings we reach out to the community of Newtown and express our heartfelt sorrow for the incomprehensible and profound loss of innocence that has affected so many."