First, he killed his mother.

Nancy Lanza’s body was found later at their home on Yoganda Street in Newtown — after the carnage at Sandy Hook Elementary School; after a quiet New England town was scarred forever by unthinkable tragedy; after a nation seemingly inured to violence found itself stunned by the slaughter of innocents.

Nobody knows why 20-year-old Adam Lanza killed his mother, why he then took her guns to the school and murdered 20 children and six adults.

But on Friday he drove his mother’s car through this 300-year-old town with its fine old churches and towering trees, and arrived at a school full of the season’s joy. Somehow, he got past a security door to a place where children should have been safe from harm.

Theodore Varga and other fourth-grade teachers were meeting; the glow remained from the previous night’s fourth-grade concert.

“It was a lovely day,” Varga said. “Everybody was joyful and cheerful. We were ending the week on a high note.”

And then, suddenly and unfathomably, gunshots rang out. “I can’t even remember how many,” he said.

There was no lock on the meeting room door so the teachers had to think about how to escape. Someone turned the loudspeaker on, so everyone could hear what was happening in the office.

“You could hear the hysteria that was going on,” Varga said. “Whoever did that saved a lot of people. Everyone in the school was listening to the terror that was transpiring.”

Gathered in another room for a 9:30 meeting were principal Dawn Hochsprung and Diane Day, a school therapist, along with a school psychologist, other staff members and a parent.

“We were there for about five minutes chatting, and we heard Pop! Pop!, Pop!” Day told The Wall Street Journal. “I went under the table.”

But Hochsprung and the psychologist leaped out of their seats and ran out of the room, Day recalled. “They didn’t think twice about confronting or seeing what was going on,” she said. Hochsprung was killed, and the psychologist was believed to have died as well.

A custodian ran around, warning people there was a gunman, Varga said.

“He said, ‘Guys! Get down! Hide!’” Varga said. “So he was actually a hero.”

Did he survive? Varga did not know.

Huddled in a corner

Police radios crackled with first word of the shooting at 9:36, according to the New York Post.

In a first-grade classroom, teacher Kaitlin Roig heard the shots. She immediately barricaded her 15 students in a tiny bathroom. She pulled a bookshelf across the door and locked it. She told the kids to be “absolutely quiet.”

“I said, ‘There are bad guys out there now. We need to wait for the good guys,’” she told ABC News.

In the gym, crying fourth-graders huddled in a corner. One of them was 10-year-old Philip Makris.

“He said he heard a lot of loud noises and then screaming,” said his mother, Melissa Makris. “Then the gym teachers immediately gathered the children in a corner and kept them safe.”

Another girl who was in the gym recalled hearing “like, seven loud booms.”

“The gym teacher told us to go in a corner, so we all huddled and I kept hearing these booming noises,” the girl, who was not identified, told NBC News. “We all started — well, we didn’t scream; we started crying, so all the gym teachers told us to go into the office where no one could find us.”

An 8-year-old boy described how a teacher saved him.

“I saw some of the bullets going past the hall that I was right next to, and then a teacher pulled me into her classroom,” said the boy, who was not identified by CBSNews.com.

‘Their child was gone’

The shooting stopped after about 15 minutes. Carefully, police searched room to room, removing children and staff from harm’s way. They found Adam Lanza, dead by his own hand.

Student Brendan Murray told WABC-TV a police officer came into his classroom and asked, “Is he in here?” and then ran out. “Then our teacher, somebody, yelled, ‘Get to a safe place.’ Then we went to a closet in the gym and we sat there for a little while, and then the police were, like, knocking on the door and they were, like, ‘We’re evacuating people, we’re evacuating people,’ so we ran out.”

Parents rushed to the scene. Family members walked away from a firehouse that was being used as a staging area, some of them openly weeping.

Gov. Dannel P. Malloy and other public officials came to the firehouse. So did clergymen like Monsignor Robert Weiss of Newtown’s St. Rose Roman Catholic Church. He watched as parents came to realize that they would never see their children alive again.

“All of them were hoping their child would be found OK. But when they gave out the actual death toll, they realized their child was gone,” Weiss said.

He recalled the reaction of the brother of one of the victims.

“They told a little boy it was his sister who passed on,” Weiss said. “The boy’s response was, ‘I’m not going to have anyone to play with.’”