NEWTOWN, Connecticut (AP) — The massacre of 26 children and adults at a Connecticut elementary school elicited horror and soul-searching around the world even as it raised more basic questions about why the gunman, a 20-year-old described as brilliant but remote, was driven to such a crime and how he chose his victims.

Investigators were trying to learn more about Adam Lanza and questioned his older brother, who was not believed to have been involved in the rampage at Sandy Hook Elementary. Police shed no light on the motive for the second-deadliest school shooting in US history.

In tight-knit Newtown on Friday night, hundreds of people packed St Rose of Lima Church and stood outside in a vigil for the 28 dead – 20 children and six adults at the school, the gunman’s mother at home, and the gunman himself, who committed suicide. People held hands, lit candles and sang “Silent Night.”

“These 20 children were just beautiful, beautiful children,” Monsignor Robert Weiss said. “These 20 children lit up this community better than all these Christmas lights we have. … There are a lot brighter stars up there tonight because of these kids.”

Lanza is believed to have suffered from a personality disorder and lived with his mother, said a law enforcement official who was briefed on the investigation.

Lanza shot his mother, Nancy Lanza, drove to the school in her car with at least three of her guns, and opened fire in two classrooms around 9:30am Friday, law enforcement officials said, speaking on condition of anonymity.

A custodian ran through the halls, warning of a gunman, and someone switched on the intercom, perhaps saving many lives by letting them hear the chaos in the school office, a teacher said. Teachers locked their doors and ordered children to huddle in a corner, duck under their desks or hide in closets as shots reverberated through the building.

The well-liked principal, Dawn Hochsprung, was believed to be among the dead. A woman who worked at the school was wounded.

Maryann Jacob, a clerk in the school library, was in there with 18 fourth-graders when they heard a commotion and gunfire outside the room. She had the youngsters crawl into a storage room, and they locked the door and barricaded it with a file cabinet. There happened to be materials for colouring, “so we set them up with paper and crayons.”

After what she guessed was about an hour, officers came to the door and knocked, but those inside couldn’t be sure it was the police.

“One of them slid his badge under the door, and they called and said, `It’s OK, it’s the police,'” she said.

A law enforcement official speaking on condition of anonymity said investigators believe Lanza attended the school several years ago but appeared to have no recent connection to it. It was not clear whether he held a job.

At least one parent said Lanza’s mother was a substitute teacher at the school. But her name did not appear on a staff list. And the official said investigators were unable to establish any connection so far between her and the school.

Lanza’s older brother, 24-year-old Ryan Lanza, of Hoboken, New Jersey, was questioned, and investigators searched his computers and phone records, but he told law enforcement he had not been in touch with his brother since about 2010.

For about two hours late Friday and early Saturday, clergy members and emergency vehicles moved steadily to and from the school. The state medical examiner’s office said bodies of the victims would be taken there for autopsies.

The gunman entered the kindergarten-through-fourth-grade school through the front door, and authorities are looking into the possibility that he shattered glass next to it to get in, police said.

He took three guns into the school – a Glock and a Sig Sauer, both semiautomatic pistols, and a .223-caliber Bushmaster rifle, according to an official. The weapons were registered to his slain mother.

Lanza and his mother lived in a well-to-do part of prosperous Newtown, about 60 miles northeast of New York City, where neighbours are doctors or hold white-collar positions at companies such as General Electric, Pepsi and IBM.

His parents filed for divorce in 2008, according to court records. His father, Peter Lanza, lives in Stamford, Connecticut, and works as a tax director for GE.

The gunman’s aunt Marsha Lanza, of Crystal Lake, Illinois, said her nephew was raised by kind, nurturing parents who would not have hesitated to seek mental help for him if he needed it.

“Nancy wasn’t one to deny reality,” Marsha Lanza said, adding her husband had seen Adam as recently as June and recalled nothing out of the ordinary.

Catherine Urso, of Newtown, said her college-age son knew the killer. “He just said he was very thin, very remote and was one of the goths,” she said.

Lanza attended Newtown High School, and several news clippings from recent years mention his name among the honour roll students.

Joshua Milas, who graduated from Newtown High in 2009 and belonged to the school technology club with him, said that Lanza was generally a happy person but that he hadn’t seen him in a few years.

“We would hang out, and he was a good kid. He was smart,” Joshua Milas said. “He was probably one of the smartest kids I know. He was probably a genius.”

In Newtown, Robert Licata said his six-year-old son was in class when the gunman burst in and shot the teacher. “That’s when my son grabbed a bunch of his friends and ran out the door,” he said. “He was very brave. He waited for his friends.”

He said the shooter didn’t utter a word.

Kaitlin Roig, a teacher at the school, said she implored her students to be quiet.

“I told them we had to be absolutely quiet. Because I was just so afraid if he did come in, then he would hear us and just start shooting the door. I said we have to be absolutely quiet. And I said there are bad guys out there now and we need to wait for the good guys to come get us out,” Roig told ABC News.

“If they started crying, I would take their face and say, `It’s going to be OK. Show me your smile,'” she said. “They said, `We want to go home for Christmas. Yes, yeah. I just want to hug my mom.’ Things like that, that was just heartbreaking.”