The gunman blasted his way through the building as young students cowered helplessly in classrooms while their teachers and classmates were shot. 18 children died at the school, officials said. 2 others died at the hospital.
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 shooter, who has been identified as 20-year-old Adam Lanza, was found dead inside the building from a self-infliced gunshot wound. Officials had earlier identified the gunman as Ryan Lanza, who they say is Adam's older brother. Sources say Adam may have been carrying Ryan Lanza's identification, causing the confusion.
According to sources, Adam Lanza shot his mother in the face and killed her at their home in Connecticut, and then drove to Sandy Hook elementary and continued his rampage.
State and federal authorities believe his mother may have once worked at the elementary school, although she was not a teacher, according to relatives, perhaps a volunteer.
Investigators said 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.
Police searched the home of Adam's brother in Hoboken. According to sources, nothing suspicious was found. Ryan Lanza was taken into custody for questioning, sources said. He is not believed to have had any involvement.
The first 911 call came in just after 9:40 a.m., stating that multiple students were trapped in a classroom with a gunman.
Youngsters and their parents described teachers locking doors and ordering the children to huddle in the corner or hide in closets when shots echoed through the building.
A custodian ran through the halls, warning of a gunman on the loose, and someone switched on the intercom, alerting people in the building to the attack by letting them hear the hysteria apparently going on in the school office.
Teacher Kaitlin Riog, who has taught first grade at the school for six years, spoke of a harrowing ordeal for her and her students. The 29-year-old Riog teaches in the first classroom when you enter the school, and she says she was in her morning meeting when she heard what sounded like automatic gunfire.
She closed and locked her door and took her students into the bathroom, which is located inside the classroom. She then had them stand on the toilet and dispenser, locked them in and pulled a tall storage unit in front to block the door.
"I felt that, in the time, I tried to be very strong for my children," she said. "I said anyone who believed in the power in the prayer, we need to pray. And those who don't believe in prayer, think happy thoughts...I told the kids I love them and I was so happy they were my students...I didn't think we were going to live."
Finally, she says there was knocking from people who claimed to be police. She didn't believe them and had them put their badges underneath the door. Still unsure, she told them that if they were cops, they could get key, which they did. The officers then helped the kids out and took them to the staging area at a nearby fire department.
"'I just want Christmas,'" she says her students told her. "'I don't want to die, I just want to have Christmas.' I said, you're going to have Christmas and Hanukkah. I tried to be positive."
Schoolchildren - some crying, others looking frightened - were escorted through a parking lot in a line, hands on each other's shoulders.
"Our hearts are broken today," a tearful President Barack Obama, struggling to maintain composure, said at the White House. He called for "meaningful action" to prevent such shootings.
The school houses more than 600 students from kindergarten through fourth grade.
The district is made up of four elementary schools, two middle schools and one high school. Schools in neighboring Monroe were also locked down as a precaution.
A vigil was held Friday night for the victims of the school massacre. It brought out hundreds of community members, including some parents who were struggling with mixed emotions after their own children survived the massacre.
With the church filled to capacity, hundreds spilled outside, some of them holding hands in circles and saying prayers. Others lit prayer candles and sang "Silent Night."
Gov. Dannel P. Malloy was among the speakers at the service inside the St. Rose of Lima Roman Catholic 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."
To make a contribution to the Newtown Memorial Fund please visit: www.newtownmemorialfund.org