For now, though, all seemed idyllic in this 300-year-old town under crystalline skies.
Adam Lanza, 20 years old, fascinated by computers and recalled by former classmates as painfully awkward, left the house in his mother's car and drove past fine old churches and towering trees. It was the holiday season, and lawns were decorated with lights and electric reindeer. It was just five miles from home to Sandy Hook Elementary, where hallways and classrooms rang with talk of Hannukah and Christmas.
Inside the music room, a group of fourth graders were watching the movie "The Nutcracker."
Theodore Varga and some other teachers were meeting. Their students, the oldest kids in the school, were in specialty classes like gym and music. 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."
The school appeared secure, it's entrance monitored by closed-circuit camera and opened only when employees in the main office buzzed somebody in. But Lanza wasted no time, breaking through the window and opening the door.
And then, suddenly and unfathomably, gunshots rang out. "I can't even remember how many," Varga said.
Someone turned the loudspeaker on, so everyone in the building 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."
The sounds reached a room where Principal Dawn Hochsprung and school therapist Diane Day along with a school psychologist, other staff members and a parent were gathered for a 9:30 meeting.
"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."
A custodian ran around, warning people there was a gunman, Varga said.
"He said, 'Guys! Get down! Hide!'" Varga said.
Did he survive? The teacher did not know.
At 9:30, Marci Benitez unlocked the door to Fun Kuts, the children's hair salon she runs in the Sandy Hook neighborhood's small downtown, and prepared for the day. Minutes later, the first police car streaked past, sirens screaming. Then another. And another. And another.
Police radios crackled with first word of the shooting at 9:36, according to the New York Post.
"Sandy Hook School. Caller is indicating she thinks there's someone shooting in the building," a Newtown dispatcher radioed, according to a tape posted on the paper's website.
In the school, Hochsprung and school psychologist Mary Sherlach leaped out of their seats and ran out of the room. Hochsprung viewed her school as a model, telling The Newtown Bee newspaper in 2010 that "I don't think you could find a more positive place to bring students to every day." She had worked to make Sandy Hook a place of safety, too, and in October, the 47-year-old principal shared a picture of the school's evacuation drill with the message "Safety first."
On this morning, Hochsprung didn't think twice about confronting the gunman. She died attempting to overtake him.
Sherlach also rushed to defend her students.
"Mary felt like she was doing God's work, working with children," her son-in-law Eric Schwartz told the South Jersey Times. She, too, was killed.
In a classroom, teacher Kaitlin Roig heard the shots and barricaded her 15 students into a tiny bathroom, sitting one of them on top of the toilet. 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.
"The kids were being so good," she said. "They asked, 'Can we go see if anyone is out there?' 'I just want Christmas. I don't want to die. I just want to have Christmas.' I said, 'You're going to have Christmas and Hanukkah.'"
One student claimed to know karate. "It's OK. I'll lead the way out," the student said.
In the school library, clerk Maryann Jacob was working with a group of 18 fourth-graders when she heard the commotion.
"We locked all our doors and then started hearing shooting," she said.
At first, she herded the children into a classroom within the library, but "when we realized the (classroom) door wouldn't lock, we had to crawl across the room into a storage room."
There, they locked the door and barricaded it with filing cabinet. There happened to be materials for coloring, "so we set them up with paper and crayons."
In the gym, crying students 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 by name, 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.
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.
"The shooting appears to have stopped," the dispatcher radioed at 9:38 a.m., according to the Post. "There is silence at this time. The school is in lockdown."
And at 9:46 a.m., an anguished voice from the school: "I've got bodies here. Need ambulances."
A half mile away, nurse Maureen Kerins was loading a broken chair into her car at about 9:45 when her cell phone rang. A friend wanted to know if her children were safe. There had been shooting at the elementary. Kerins' five kids are older, but she jumped in her car and raced to Sandy Hook. When she told police she was a nurse, they let her through.
As she approached the school, teachers were leading their children out single file, each had their hand on another's shoulder.
"It was very orderly. They weren't even running, they were just walking, following their teacher," she said. "Nobody was screaming. Parents were racing around looking for their kids, but the kids were just in line, following their teacher. Some were crying, but mostly they were calm."
She made a couple more trips with children, then went back to the school and waited with another nurse and a pediatrician to help treat the wounded. None ever came out.
"You expected them to be bringing out more kids," said Debbie Leidlein, the school board president, who was home sick but rushed to the school when she heard the news, "and it just wasn't happening."
Kerins waited for two hours, watching as police officers came and went but never brought any more children outside.
"Finally they said to us they didn't need us anymore. We knew it was bad."
Carefully, police searched room to room, removing children and staff from harm's way. They found Adam Lanza, dead by his own hand after shooting up two classrooms. No officer fired a gun.
Student Brendan Murray told WABC-TV it was chaos in his classroom at first after he heard loud bangs and screaming. A police officer came in 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."
As they were led away, children were warned to close their eyes so they would not see the gruesome aftermath of the attack.
Parents rushed to the scene. Family members walked away from a firehouse that was being used as a staging area, some of them weeping. One man put his arms around a woman as they walked down the middle of the street, oblivious to everything around them.
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.'"
Long into the night, Leidlein sat with parents who had lost their children, trying to do what little she could to offer consolation.
"They were asking why. They can't wrap their minds around it. Why? What's going on?," she said. "And we just don't have any answers for them."
Jocelyn Noveck reported from New York. Jim Fitzgerald, Pat Eaton-Robb, Matt Apuzzo and Adam Geller in Newtown and Bridget Murphy in Boston contributed to this report.