The victims of the Sandy Hook School school shooting in Connecticut were shot multiple times with a semi-automatic rifle, the medical examiner has said, and he called the injuries "devastating".
The details came as police released the identities of the 26 victims at Sandy Hook Elementary school. All of the 20 children killed were six or seven years old.
Police said they had found "very good evidence" they hoped would answer questions about the motives of the gunman, 20-year-old Adam Lanza, described as brilliant but remote, who forced his way into the school in one of the world's worst mass shootings.
Witnesses said Lanza did not speak during the attack and later killed himself.
The Lanza family released a statement Saturday night expressing "our heartfelt sorrow".
The medical examiner, 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."
Townspeople took down Christmas decorations and sang Silent Night at memorials. World reaction was swift and emotional, any many immediately thought of Dunblane - a 1996 shooting in a small Scottish town which killed 16 primary school children and prompted a campaign that ultimately led to tighter gun controls.
Pressure to take similar action built on president Barack Obama, whose comments on the tragedy were one of the most outwardly emotional moments of his presidency.
He has promised "meaningful action" on the issue of mass shootings, "regardless of the politics", but national debates after past shootings have led to little change.
Stunned residents and exhausted officials continue to fill in the details of the attack. Town education officials said the well-liked school principal, Dawn Hochsprung, was killed while lunging at the gunman as she tried to overtake him.
In Newtown, a small and picturesque New England community about 60 miles north east of New York City, nearly everyone seemed to know someone who died. Investigators said they believe Lanza attended the school many years ago, but they had no explanation for why he went there on Friday.
Connecticut state police Lieutenant Paul Vance told reporters that investigators had found "very good evidence" about the gunman, but another law enforcement source said 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, survived after being shot - an unusually small number in a mass shooting - and Lt Vance said her comments would be "instrumental".
Detectives said two pistols, a Glock and a Sig Sauer, and a .223-calibre Bushmaster rifle were found in the school and a fourth weapon was found outside the school.
Authorities said Lanza had no criminal history. It was not clear whether he had a job. Lanza was believed to have suffered from a personality disorder, said sources. Lanza attended Newtown High School, and several news clippings from recent years mention his name among the honour roll students.
On Friday morning, Lanza shot his mother Nancy at their home, drove to the school in her car and shot up two classrooms, law enforcement officials said.
The school's entrance was monitored by close-circuit camera and opened only when employees in the main office buzzed somebody in, but Lanza broke through the window and opened the door.
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.
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," Ms Lanza said, adding her husband had seen Lanza as recently as June and recalled nothing out of the ordinary.
Olivia DeVivo recalled that Lanza always came to school carrying a briefcase and wearing his shirt buttoned all the way up. "He was very different and very shy and didn't make an effort to interact with anybody," she said.
"You had yourself a very scared young boy who was very nervous around people," said Richard Novia, who was adviser to the school's Tech Club, of which Lanza was a member.
Mr Novia said Lanza also had a strange bodily condition: "If that boy would've burned himself, he would not have known it or felt it physically."
When people approached Lanza in the hallways, he would press himself against the wall or walk in a different direction, clutching his black case "like an eight-year-old who refuses to give up his teddy bear", said Mr Novia.
Even so, Mr Novia said his main concern was that Lanza might become a target for teasing or abuse, not that he might become a threat.
Sandy Hook school will be closed next week - some parents cannot conceive of sending their children back, Board of Education chairwoman Debbie Leidlein said.
President Barack Obama will attend a memorial service later today in Newtown.
Hours after the shooting, a tearful Mr Obama said he grieved first as a father. In those remarks and later in his Saturday radio address, he called for "meaningful action" to prevent such shootings, but did not say what it should be.
Mr Obama's visit to Newtown for an interfaith vigil will be the fourth time he has travelled to a city after a mass shooting.
The president had planned to travel to Maine on Wednesday for an event promoting his positions in "fiscal cliff" negotiations, but the White House cancelled that trip because of the shooting.
A gunman at a Connecticut elementary school has killed 26 people, including 20 children - one of the world's worst mass shootings. Here are some others: