SET on the brow of a gently sloping hill, surrounded by two acres of woodland and well-tended lawns, the spacious property looks like an American family's dream home.
A wide veranda has views across the gardens. A swimming pool, flanked by a white pool house, sits at the back of the two-storey building.
Yet in recent years, all was not well behind the door of 36 Yogananda Street in the affluent Connecticut community of Newtown.
In 2009, Nancy and Peter Lanza divorced after 28 years of marriage. The break-up was traumatic, leaving the couple's sons devastated. Ryan Lanza was living away at university, meaning that his brother, Adam, at 20, four years younger, was left at home alone with their mother at their $565,000 (€430,000) house.
He was not well known to neighbours, who described him as reclusive and troubled.
When news broke on Friday of the massacre at a primary school in the town, and Ryan Lanza was hastily identified as the killer, those acquainted with the family knew they had named the wrong brother.
"Adam Lanza has been a weird kid since we were five years old," said Tim Dalton, a neighbour and former classmate, on Twitter. "As horrible as this was, I can't say I am surprised."
A family insider said: "This was a deeply disturbed kid. He certainly had major issues. He was subject to outbursts, from what I recall."
Another family friend said Lanza had acted as though he was immune to pain.
"A few years ago when he was on the baseball team, everyone had to be careful that he didn't fall because he could get hurt and not feel it," said the friend. "Adam had a lot of mental problems."
Ryan Lanza reportedly told police that his brother had autism or Asperger's syndrome, and a personality disorder. He gave no details, but such a disorder is often linked with violence and criminal behaviour.
Studies have suggested that around 50 per cent of the prison population meet the criteria for diagnosis. Those with such disorders are more likely to embark on impulsive, risk-seeking behaviour in an attempt to escape feeling empty or emotionally void.
In such cases, they are likely to have little regard for the consequences of their actions and are unlikely to experience fear.
As the news was breaking, Ryan was at work with the accountancy firm Ernst & Young, sitting at his desk in Times Square, New York.
To his horror, the 24-year-old found that his name was flashing up on the TV news networks, wrongly accusing him of the massacre. He fled the office, jumping on a bus to return to the house he shares in New Jersey.
Shaken, he told his neighbour in an online message that he thought his mother was dead and he knew who was responsible for the multiple murder.
"It was my brother," he said.
Ryan also said he had not seen his brother since 2010.
Some people with personality disorders have a more limited emotional range and can miss social cues, making it more difficult for them to communicate and feel empathy with others. Difficulties communicating can cause frustration, which can spill over into aggression.
However, several studies have found that violence is no more common in those diagnosed with personality disorders than they are in the general population. Asperger's is a type of autism which is more commonly diagnosed in those with higher than average intelligence. And Lanza was said by classmates to be fiercely intelligent.
"You could tell he was, I would say, a genius," said Miss Israel. "There was something that was above the rest of us."
He'd correct people's Latin homework when they were aged around 14, and at 16 was among the list of top students in his English class, studying Of Mice And Men and The Catcher In The Rye – the classic tale of disaffected youth.
"It was almost painful to have a conversation with him because he felt so uncomfortable," said Olivia DeVivo, who sat behind him in English. "I spent so much time in my English class wondering what he was thinking."
"He didn't have any friends, but he was a nice kid if you got to know him," said Kyle Kromberg, now studying business administration at Endicott College in Massachusetts. He studied Latin with Lanza.
"He didn't fit in with the other kids," he said. "He was very shy. He wouldn't look you in the eyes when he talked. He didn't really want to lock eyes with you for very long."
He was also a technical whizz kid, keen on computers and video games, and part of a group who would meet up for computer programming get-togethers.
"My brother has always been a nerd," Ryan said.
Catherine Urso, who was attending a vigil on Friday evening in Newtown, said her college-age son knew the killer and remembered him for his alternative style.
"He just said he was very thin, very remote and was one of the goths," she said.
The siblings certainly carved out different paths in life. Ryan went to university; followed his father into finance; was living with friends in an attractive red-brick property in New Jersey.
Indeed, when the tragedy of Friday was unfolding, one of his housemates, Jessica O'Brien, wrote on Facebook: "Do you need anything ready for when you get home? Can I set anything out for you to grab and go? Anything else I can do?"
By contrast, Adam Lanza had few friends and, as a child, went to great trouble not to mix with his fellow students at his state school. A Newtown resident also suggested he was home-schooled for some time.
"I always saw him walking alone, sitting on his own at a table or on the bus. Most of the time I saw him he was alone," said Alex Israel, who was at school with him as a young girl. "He was really quiet. A little fidgety, uneasy."
Her mother, Beth Israel, said: "I know he had issues. He was a really troubled kid... a very quiet kid, a shy kid, maybe socially awkward."
He was not on Facebook, unusually for any Westerner of his generation, and neither did he appear in his 2010 High School Yearbook. Instead is written: "Camera shy."
Forty miles from Newtown, in the well-heeled Connecticut city of Stamford, Lanza's father, Peter – who was divorced from the boys' mother, Nancy – was returning home on Friday afternoon. An academic who a year ago was appointed vice-president of taxes for energy investment firm GE Energy Financial Services, Mr Lanza wound down the window of his Mini Cooper and asked the person outside his home how he could help her.
"I explained that I'd been told someone at his address had been linked to the shootings in Newtown," said Maggie Gordon, a reporter from the local newspaper. "His expression twisted from patient, to surprise, to horror."
Mr Lanza had moved out in 2008, remarrying a University of Connecticut librarian in January last year. He was said to have last seen Adam in June.
The shy young man had taken the divorce badly.
"The kids seemed really depressed" by the break-up, said Ryan Kraft, 25, who stayed with Adam when Mrs Lanza went out. "He would have tantrums," Mr Kraft said. "Much more than average."
Mr Lanza's lawyer, Gary Oberst, said: "He was very upset that he was getting divorced, but he didn't want to take it out on anybody.
"He did more than he had to with the divorce. When he came in to consult with me, I said, 'This is what your obligation is'. And he said, 'That's not enough. I want to do more'."
Mr Lanza agreed to pay $240,000 (€182,000) a year to his ex-wife, who seemed to live in comfort with Adam. There were also suggestions that she was unable to work.
Marsha Lanza, aunt to the boys, described Mrs Lanza as a good mother and kind-hearted. Mrs Lanza would host games of dice, or else venture out to visit her neighbours. The house was immaculate; the swimming pool behind the house well maintained.
But Mrs Lanza was also, according to friends, an avid gun collector. Dan Holmes, owner of a local landscaping firm, said Mrs Lanza once showed him a "high-end rifle" that she had bought, adding, "She said she would often go target shooting with her kids."
The gun used to shoot Mrs Lanza was her own.
Yet, perhaps predictably, the owner of the local rifle range was defiant.
Richard Dravis, who gives shooting training at Wooster Mountain rifle range, 15 miles from the school, said: "We don't train crazy people. I think that if we would address the mental health issue here we could possibly do something in the future. But we can't count the number of rounds in the magazine of a nut head."