Americans are agonizing over the murder spree by Adam Lanza, who was known by school mates as intelligent – but strange.

On leafy Yogananda Street, home to Nancy Lanza and her son Adam, one woman named Megan, age 20 and who declined to divulge her last name, told AFP, “He was a weird kid as a child, but he was just quiet. We never knew his real personality. He was just himself.

“I knew he lived in the area. But he fell off of the radar halfway through middle school, maybe seven or eight years ago,” she said in the usually sleepy, wealthy town of Newton, Connecticut.

Lanza, 20, is thought to have used a Bushmaster .233 rifle – designed for shooting people in military assaults – owned by his mother Nancy. He killed 20 children, including six-year-old Jewish boy Noah Posner,  and six adults. Police believe Adam murdered his mother, shooting her in the face before heading to the school.

There he unleashed a wave of terror authorities say was the deadliest massacre at a US grade school, shocking the United States with the apparently senseless and staggering targeting of one innocent child after another.

“As long as I remember he was very intellectually sound at school,” Megan said of her old classmate Adam.

Getting to Nancy Lanza’s home is almost impossible; police have it closed off as a second crime scene in the town due to her murder.

It also is hard to find neighbors able or willing to speak about the family in a neighborhood of plush, sprawling single family homes with huge lawns down rolling hills.

Another young man who lives nearby and also refused to give his name rode over on a skateboard and spoke about Adam Lanza.

“I knew Adam cause I went to school in the same bus,” he told AFP privately. “We ate lunch, played chess. He was very smart.

“He was kind of kid that, in the computer classes, where me and other kids had a hard time ’cause we had two seconds to do something. Then he would just go in and get it done.”

The young man said he was unaware of any talk of weapons in the Lanza home, before popping his hood over his head and skating off away from photographers.

While school friends recalled facets of Adam’s personality, the family was basically not well known to many neighbors, like relative newcomers the Strocchia family.

“They are a mystery. Nobody knows about them. A lot of the people in this neighborhood know each other. It was very hard to find that I didn’t know them and nobody on the block knew them,” said Len Strocchia, 46, who has lived on the same street as the Lanzas for six years.

Though he was remembered as a shy and awkward boy, Lanza had not apparently given any warning sign that he could be a mass murderer in the making.