The mother of the Connecticut gunman taught him to handle firearms to instill him with a "sense of responsibility" and even took him to the shooting range days before the atrocity, it was claimed on Monday.
It also emerged that Adam Lanza was so emotionally detached in his teens that school officials assigned him a psychiatrist. They feared that he might harm himself, but did not regard him as a danger to others.
Lanza, a computer "nerd" who was said to have had a development disorder, "loved being careful" with guns and "made it a source of pride", according to friends of his mother Nancy.
Lanza, a gun enthusiast who owned at least five weapons and was the first victim of his rampage, introduced Adam and his older brother Ryan to firearms at a young age. Indeed, she took her younger son to a local firing range just days before the rampage, CNN reported.
"She told me she had wanted to introduce them to the guns to teach, especially Adam, a sense of responsibility," a friend told NBC television. "Guns require a lot of respect and she really tried to instill that... and he took to it. He loved being careful with them. He made it a source of pride."
The friends, who called Lanza a vivacious "country girl", insisted that the weapons would have been locked up at the home where she had lived alone with her youngest son after Ryan moved away and her divorce from their father, Peter. "She was very responsible," said one.
Lanza was clearly aware of warning signs about her son's troubles from a young age. Indeed, she cautioned a babysitter who looked after him when he was nine or 10 never to turn his back on the child.
Ryan Kraft, who was in his mid-teens at the time, said she told him "to keep an eye on him at all times... to never turn my back, or even to go to the bathroom or anything like that".
Kraft recalled the boy as highly intelligent, introverted and extremely focused. "It was like he was in his own world," he said.
Lanza was a loving mother who was very involved in her children's lives, he said.
Despite all her efforts, she had just confided to another friend recently that she feared she was "losing her son" as his mental health deteriorated.
Less than a week before the rampage, she shared her concerns with another regular at her favourite Newtown restaurant. "She said it was getting worse," the friend told the New York Daily News. "She was having trouble reaching him."
Echoing comments by former schoolmates of Adam, the friend also said that Adam seemed to have no sensation of pain. "Nancy told me he was burning himself with a lighter. In the ankles or arms or something," he said. "It was like he was trying to feel something."
Staff at Newtown High School had appointed a psychiatrist for him when he was about 15. "At that point in his life, he posed no threat to anyone else," said Richard Novia, former director of security for the local education district. "We were worried about him being the victim or that he could hurt himself."
Lanza was described by many as highly intelligent. He attended some classes at a university in Connecticut when he was just 16.
His mother was recently considering a move across the country to Washington state after finding a college that she thought might suit her son.