"The majority of those who died were children beautiful little kids between the ages of 5 and 10 years old," Obama told a White House news briefing, struggling to keep his composure. He promised "meaningful action" on the issue of mass shootings, "regardless of the politics."
Stunned residents and exhausted officials continued Saturday (local time) to fill in the details of the attack.
The medical examiner said victims were shot multiple times by a semiautomatic rifle and he called the injuries "devastating" and the worst he and colleagues had ever seen.
Police have begun releasing the identities of the dead. All of the 20 children killed were 6 or 7 years old.
The examiner, Dr. H. Wayne Carver, said he examined seven of the children killed, and two had been shot at close range. When asked how many bullets were fired, he said, "I'm lucky if I can tell you how many I found".
The school's well-liked principal, Dawn Hochsprung, was killed while lunging at the gunman as she tried to overtake him, town officials said. Board of Education chairwoman Debbie Liedlien said administrators were coming out of a meeting when the gunman forced his way into the school, and they ran toward them.
Asked whether Hochsprung is a hero, the chairman of the town's Legislative Council, Jeff Capeci, said, "From what we know, it's hard to classify her as anything else".
In Newtown, a small and picturesque New England community about 95 kilometers northeast of New York City, 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.
Just 10 days before Christmas Eve, people held hands, lit candles and sang "Silent Night."
"People in my neighborhood are feeling guilty about it being Christmas. They are taking down decorations," said Jeannie Pasacreta, a psychologist who was advising parents on how to talk to their children.
Connecticut state police Lt. Paul Vance told reporters Saturday that investigators had found "very good evidence" and hoped it would answer questions about the gunman's motives. Vance would not elaborate.
However, another law enforcement official, speaking on condition of anonymity, said that investigators had found no note or manifesto of the sort they have come to expect after murderous rampages.
Just one person, a woman who worked at the school, was shot and survived an unusually small number in a mass shooting and Vance said her comments would be "instrumental".
Investigators had not found evidence after talking with state gun dealers and gun ranges that the gunman trained for the attack or was an active member of the recreational gun community, US Bureau of Alcohol, Tobacco and Firearms spokeswoman Ginger Colbrun said.
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 and shot up two classrooms Friday morning, 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 or hide in closets as shots echoed through the building.
Maryann Jacob, a clerk in the school library, was with 18 students when they heard gunfire outside the room. She had the children crawl into a storage room, and they locked the door and barricaded it with a file cabinet. There happened to be materials for coloring, "so we set them up with paper and crayons".
After what she guessed was about an hour, officers came to the door and knocked.
"One of them slid his badge under the door, and they called and said, 'It's OK, it's the police,"' Jacob said.
A law enforcement official said a Glock and a Sig Sauer, both pistols, and a .223-caliber Bushmaster rifle were found in the school and a fourth weapon was found outside the school, and that investigators were going to shooting ranges and gun stores to see if Lanza had frequented them. The official was not authorized to discuss information with reporters and spoke on condition of anonymity.
Adam Lanza attended Newtown High School, and several news clippings from recent years mention his name among the honor roll students.
At least one parent said Lanza's mother was a substitute teacher there. 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, but a law enforcement official said he was not believed to have had a role in the rampage. He told law enforcement he had not been in touch with his brother since about 2010. The official spoke on the condition of anonymity because they were not authorized to discuss the unfolding investigation.
The gunman's aunt Marsha Lanza 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 gunman. "He just said he was very thin, very remote," she said.
Joshua Milas, who graduated from Newtown High in 2009 and belonged to the school technology club with him, said Adam 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."
The community also turned its focus Saturday to the young children who had witnessed the attack. Police had students to close their eyes as they were led from the building so they wouldn't see the blood and broken glass. In a photo by the local Newtown Bee newspaper that quickly became the defining image of the attack, children some crying, many looking frightened were escorted through a parking lot in a line, hands on one another's shoulders.
Robert Licata said his 6-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.
"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 were just heartbreaking."
-AP
