Updated Dec. 15, 2012, 1:42 a.m. ET
A man killed his mother at their home and then opened fire Friday inside an elementary school, massacring 26 people, including 20 children, as youngsters cowered in fear to the sound of gunshots reverberating through the building and screams echoing over the intercom.
The bodies of most of the children killed in the morning remained inside Sandy Hook Elementary School in Newtown, Conn., Friday evening, along with the bodies of six adults and the gunman himself, Connecticut State Police spokesman Lt. Paul Vance told "CBS Evening News" anchor Scott Pelley.
As SWAT teams surrounded the school, state troopers moved students to safety. Some children were told to close their eyes to protect them from seeing the carnage. The police eventually found the gunman dead from a self-inflicted wound, the police said.
Among the dead was the school's principal, Dawn Hocksprung. One teacher was wounded but survived.
The attack, coming less than two weeks before Christmas, was the nation's second-deadliest school shooting, exceeded only by the Virginia Tech massacre that left 33 people dead in 2007.
"This is most definitely the worst thing that we have experienced in town - tragic," Newtown police Lt. George Sinko told reporters.
"Evil visited this community today," Connecticut Gov. Dannel Malloy told reporters at a news conference attended by Sen. Richard Blumenthal and Sen.-elect Chris Murphy, who represent the state.
A source familiar with the investigation identified the shooter as 20-year-old Adam Lanza, CBS News investigative producer Pat Milton reports. Law enforcement sources had earlier told CBS News that the gunman was Ryan Lanza, Adam Lanza's older brother.
Ryan Lanza is being questioned by authorities in New Jersey, Milton reports. As of Friday evening, Ryan Lanza was not considered a suspect, CBS News correspondent Bob Orr reports.
Police shed no light on the motive for the attack. The gunman, Adam Lanza, was believed to suffer from a personality disorder and lived with his mother, said a law enforcement official who was briefed on the investigation but was not authorized to discuss it.
Law enforcement officials speaking on condition of anonymity said that Lanza fatally shot his mother, Nancy Lanza, then drove to the school in her car with at least three guns, including a high-powered rifle that he apparently left in the back of the vehicle, and shot up two classrooms around 9:30 a.m. The New York Times reported that Lanza wore combat gear.
The shooting took place in two classrooms, Vance told reporters at an afternoon news conference. Eighteen children died at the school, some as young as 5. Two more died after being transported to area hospitals, he 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 the place.
The school teaches about 700 students between kindergarten and fourth grade.
On Friday night, hundreds of people packed a Newtown church and stood outside in a vigil for the victims. People held hands, lit candles and sang "Silent Night" at St. Rose of Lima church.
At the vigil, the priest said the altar holds 26 candles, all of which were lit in memory of the victims. Lyrics of the last hymn of the ceremony rang out: "I will raise him up on eagle's wings."
The parish priest, Robert Weiss, said he spent much of Friday with victims of the families but he could not give them any answers about what happened.
David Connors, the father of three triplets at the school, said at a vigil that his children were taken into a closet during the lockdown.
"My son said he did hear some gunshots, as many as 10," he said. "The questions are starting to come out. `Are we safe? Is the bad guy gone?"'
Adam Lanza and his mother lived in a well-to-do part of Newtown where neighbors are doctors or hold white-collar positions at companies such as General Electric, Pepsi and IBM.
At least three guns were found — a Glock and a Sig Sauer, both pistols, inside the school, and a .223-caliber rifle in the back of a car, authorities said. A law enforcement official speaking on condition of anonymity said some of the guns used in the attack may have belonged to Lanza's family. His mother had legally registered four weapons, his father two.
Authorities also recovered three other guns — a Henry repeating rifle, an Enfield rifle and a shotgun. It was not clear exactly where those weapons were found.
President Obama promised action to prevent such tragedies again but did not say what that would be.
"Our hearts are broken today for the parents and grandparents, sisters and brothers of these little children and for the families of the adults who were lost," an emotional Mr. Obama said Friday afternoon in a statement delivered from the White House briefing room.
"Our hearts are broken for the parents of the survivors, as well," said Mr. Obama. "For, as blessed as they are to have their children home tonight, they know that their children's innocence has been torn away from them too early, and there are no words that will ease their pain."
White House spokesman Jay Carney said Mr. Obama was informed of the shooting at 10:30 a.m. ET by homeland security adviser John Brennan.
A dispatcher at the Newtown Volunteer Ambulance Corps said a teacher had been shot in the foot and taken to Danbury Hospital.
State police said Newtown police called them around 9:40 a.m.
A photo posted by The Newtown Bee newspaper showed a group of young students — some crying, others looking visibly frightened — being escorted by adults through a parking lot in a line, hands on each other's shoulders.
An 8-year-old student told CBS New York station WCBS-TV he was on his way to the school's office when he saw the gunman.
"I saw some of the bullets going down the hall and then a teacher pulled me into her classroom," the boy said.
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.
Stephen Delgiudice said his 8-year-old daughter heard two big bangs and teachers told her to get in a corner. His daughter was fine.
"It's alarming, especially in Newtown, Connecticut, which we always thought was the safest place in America," he said.
Delgiudice's daughter told him that she heard the loudspeaker come on and swearing being broadcast over it, Delgiudice told CBS News. That prompted the teacher to lock the classroom door.
"That's basically what saved their lives, I think," Delgiudice told CBS News.
Theodore Varga was in a meeting with other fourth-grade teachers when he heard the gunfire. He said someone had turned on the intercom so that "you could hear people in the office. You could hear the hysteria that was going on. I think whoever did that saved a lot of people. Everyone in the school was listening to the terror that was transpiring."
Also, a custodian ran around, warning people there was someone with a gun, Varga said.
"He said, `Guys! Get down! Hide!"' Varga said. "So he was actually a hero." The teacher said he did not know if the custodian survived.
Lisa Bailey, a Newtown resident with three children in Newtown schools, told CBSNewYork.com, "Newtown is a quiet town. I'd never expect this to happen here. It's so scary. Your kids are not safe anywhere."
Mergim Bajraliu, 17, heard the gunshots echo from his home and ran to check on his 9-year-old sister at the school. He said his sister, who was fine, heard a scream come over the intercom at one point. He said teachers were shaking and crying as they came out of the building.
"Everyone was just traumatized," he said.
Mary Pendergast, who lives close to the school, said her 9-year-old nephew was in the school at the time of the shooting, but wasn't hurt after his music teacher helped him take cover in a closet.
Richard Wilford's 7-year-old son, Richie, is in the second grade at the school. His son told him that he heard a noise that "sounded like what he described as cans falling."
The boy told him a teacher went out to check on the noise, came back in, locked the door and had the kids huddle up in the corner until police arrived.
"There's no words," Wilford said. "It's sheer terror, a sense of imminent danger, to get to your child and be there to protect him."