How Adam Lanza carried out the Newtown shootings

Less than two weeks before Christmas, quaint Newtown, Conn., is dressed for the holidays.

On Yogananda Street, wreaths hang above doorways and holiday lights are strung along eaves.

In a yellow Colonial on a quiet, wooded lot, one of the nation's worst massacres begins. While the motive remains a mystery, this is an account of what happened, based on reports from authorities, survivors and town officials.

The gunman, Adam Lanza, 20, shoots and kills his mother, Nancy, 52, inside the  four-bedroom home they share.

About 9 a.m. Friday, leaving her body behind, he grabs at least four guns, all registered to his mother: two rifles and two pistols -- a Glock and a Sig Sauer.

Dressed in black fatigues and military vest, he drives his mother's black Honda sedan 4½ miles to Sandy Hook Elementary School, which he once attended.

The weather is crisp and clear as Lanza makes his way through the 300-year-old town, with its historic churches and towering trees. At the school, he parks in the fire lane in front of the main entrance.

The school appears secure, its entrance monitored by a closed-circuit camera. But Lanza, taking three weapons with him, forces his way in.

Inside, more than 600 children and their teachers are beginning their day. Fourth graders, the oldest children in the school, are in gym and music classes. Some are watching the movie "The Nutcracker."

Principal Dawn Hochsprung, school therapist Diane Day, other staff members and a parent are having a meeting.

Shortly before 9:30, Lanza bursts into the administrative offices and opens fire.

"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."

As Lanza moves down the hall, Hochsprung lunges at him, trying to stop the shooting. The act of heroism costs the principal her life.

But a warning sounds throughout the school. The public address system is on loud enough for staff and students to hear gunshots and screams.

In Jaclyn Lloyd's gym class, Elise Beier and her fourth-grade classmates huddle briefly in a corner, before teachers usher them into a hiding place -- a storage closet. They have no idea where the gunman is.

"You didn't know what he was doing," recalled Elise, 10. "He could come in here; he could not."

In a first-grade classroom, teacher Kaitlin Roig also hears the shots. She rushes her 15 students into a bathroom. She locks the door and barricades it with a bookshelf, telling the students to be "absolutely quiet."

"I said, 'There are bad guys out there now. We need to wait for the good guys,' " Roig told ABC News.

"The kids were being so good. 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 says he knows karate. "It's OK. I'll lead the way out," the boy tells Roig.

Lanza next enters Room 10, a first-grade classroom where teacher Victoria Soto, 27, hid her students in closets and cabinets. She tells the gunman the kids are in the gym and is fatally shot.

As the rampage unfolds, local police receive their first 911 call, at 9:31, from inside the school.

Newtown officers begin rushing to the shooting scene. Surrounding police agencies and the Connecticut State Police are alerted. Troopers, on-duty and off-duty, scramble to respond.

Meanwhile, Lanza, wielding an assault rifle, moves on to a second first-grade classroom. He sprays bullets at close range, killing a number of children -- many of them 6 years old.

As students and teachers in other parts of the building cower in fear, or sprint to safety, the attack suddenly ends.

"The shooting appears to have stopped," a dispatcher says over the police radio at 9:38. "There is silence at this time. The school is on lockdown."

Arriving police enter the school, see the carnage, and call for medical help. "Send a bus," a dispatcher says a short time later, referring to an ambulance.

It's too late to save the victims at the school: 20 children and six adults.

Officers didn't have to fire a shot. They found Lanza dead from a self-inflicted gunshot wound.

With Scott Eidler, Matthew Chayes and AP