All six adults killed at the school were women. Of the 20 children who were shot to death, eight were boys and 12 were girls. All the children were ages 6 or 7.
See the complete list of victims' names released by Connecticut police
Police say the suspected gunman, identified by authorities as 20-year-old Adam Lanza, barged into Sandy Hook Elementary School Friday morning and shot and killed the children and adults, including the school's principal and psychologist.
Peter Lanza, Adam Lanza's father, addressed the shooting in a statement on Saturday.
"Our hearts go out to the families and friends who lost loved ones and to all those who were injured," he said. "Our family is grieving along with all those who have been affected by this enormous tragedy. No words can truly express how heartbroken we are. We are in a state of disbelief and trying to find whatever answers we can. We too are asking why. We have cooperated fully with law enforcement and will continue to do so. Like so many of you, we are saddened, but struggling to make sense of what has transpired."
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. Police say the shooting happened in one section of the school in two rooms.
Town officials said Principal Dawn Hochsprung died while lunging at the gunman in an attempt to overtake him. A woman who worked at the school was wounded.
The slain psychologist was identified by ABC News as Mary Sherlach. In a statement, Sherlach's eldest daughter, Maura Schwartz, described her mother as a "wonderful, caring woman who was invested in her students."
Sherlach's son-in-law added, "Mary felt like she was doing God's work by helping children."
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Authorities had previously said the gunman was let inside the school, but Lt. Paul Vance with Connecticut State Police said during a Saturday morning news conference that it appears Lanza forced his way into the school.
Investigators say Lanza had also shot and killed his mother at her home before he drove to the school to continue the shooting spree then took his own life.
The question on the world's mind is, why? Vance touched on that topic at the news conference, saying investigators have found "very good evidence" at both the school and Lanza's mother's home. He said that evidence is beginning to paint a complete picture of the motive. He refused to elaborate on exactly what was found at the crime scenes.
The victims' families have all been notified. The family of one of the students killed released the following statement Saturday morning:
"We are greatly saddened by the loss of our beautiful daughter, Catherine Violet and our thoughts and prayers are with the other families who have been affected by this tragedy...We ask that you continue to pray for us and the other families who have experienced loss in this tragedy," said the family of Catherine Hubbard, a first-grader killed at Sandy Hook Elementary School.
Sources told ABC News that after Lanza shot his mother in the face, he left the house armed with at least two semi-automatic handguns, a Glock and a Sig Sauer, and a semi-automatic rifle. He was also wearing a bullet-resistant vest.
ABC News reports Lanza's mother and father were both registered gun owners. Authorities said they recovered more than three weapons at the scene. ABC News reports that those weapons included two semi-automatic handguns registered to his mother. A Bushmaster rifle also registered to his mother was discovered outside the school in a car.
His mother was reportedly a teacher's aide at Sandy Hook. According to court records, Lanza's parents divorced in 2009. When they first filed for divorce in 2008, both Peter and Nancy Lanza were ordered to undergo a parenting education program, reports ABC News.
Adam was 17 at the time of the divorce. He continued to live in Newtown with his mother. His father now lives in his Stamford, Conn. with his second wife.
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Earlier in the investigation, federal sources initially identified the suspect as Adam's older brother Ryan Lanza, 24. Federal sources told ABC News that identification belonging to Ryan Lanza was found at the shooting scene. Ryan Lanza soon took to Facebook to say he was alive and not responsible for the shooting. He was later questioned by police.
Neighbors and former classmates describe Adam Lanza as very bright but socially awkward and deeply troubled.
President Barack Obama was briefed on the shooting by FBI Director Robert Mueller. Mr. Obama ordered flags flown at half staff at all federal and military buildings and installations.
"Our hearts are broken today," Mr. Obama said as he addressed the nation. A tearful president said there's "not a parent in America who doesn't feel the overwhelming grief that I do."
Watch Pres. Obama's national address about the Sandy Hook shootingFriday's shooting came three days after masked gunman Jacob Roberts opened fire in a busy mall in Clackamas, Ore., killing two before turning the gun on himself.
Sandy Hook Elementary School includes 450 students in grades K-4. The town is located about 12 miles east of Danbury, Conn.
President Barack Obama used his weekly address to talk about the tragedy in Connecticut. He tearfully addressed the nation Friday, shortly after the mass shooting. Mr. Obama is expected to travel to Newtown on Sunday to visit with the victims' families and thank first responders. He will also speak at a nighttime vigil.
Friday night, hundreds of people in tight-knit Newtown packed St. Rose of Lima Church and stood outside in a vigil for the victims. People held hands, lit candles and sang "Silent Night." A truck full of flowers was delivered to the school early Saturday morning.
See photos from the Sandy Hook school shooting in Connecticut
As a result of the shooting, police across the United States, including in Los Angeles, stepped up school security. LAPD officers provided additional patrols to city schools throughout the day, and the patrols are expected to continue when students return to school in January.
To make a contribution to the Newtown Memorial Fund please visit: http://www.newtownmemorialfund.org/
Reporter Carlos Granda is in Newtown, Conn. Look for his live reports throughout the weekend on ABC7 Eyewitness News.
ABC News and the Associated Press contributed to this report.
