NEWTOWN, Conn. -- The shooter at Sandy Hook Elementary School forced his way into the school Friday morning and gunned down his victims using a semiautomatic rifle, inflicting multiple wounds to all 20 small children, the state's chief medical examiner said Saturday evening.

Autopsies showed Adam Lanza, 20, did all of his killing with the .223 caliber Bushmaster rifle, not the two 9 mm handguns also found inside the school. Early reports said the handguns were used in the shooting and the rifle was found in his vehicle outside the school.

Those three guns are believed to belong to his mother, 52-year-old Nancy Lanza, who police said was shot in the head by her son at their shared Newtown home before he drove to the school.

Police so far have been unwilling to shed light on why the 2010 Newtown High School graduate, described in reports as a nice kid who liked video games, set his sites on the local elementary school. Several reports have indicated the man had a mental disorder, but Lt. Paul Vance of the Connecticut Police Department would not confirm a motive.

Authorities released the names of the victims Saturday evening after working all night and day to identify the bodies. Among the 26 killed -- the second largest mass shooting on U.S. soil -- eight were boys and 12 were girls, all between the ages of 6 and 7.

Six adult females who worked at the school were also killed, including Principal Dawn Hochsprung, 47, who witnesses credited with heroically confronting Lanza after he started shooting. Two adults were taken to separate hospitals and are fine, Vance said. Lanza also took his own life in the school building.

Chief Medical Examiner H. Wayne Carver said the seven victims he personally autopsied were struck three to 11 times by rounds from Lanza's rifle.

Asked if they suffered, Carver replied: "If they did, it wasn't for very long."

Police said that Lanza forced his way into the building around 9:30 a.m., likely by shattering a glass pane next to the front door, before opening fire on two first-grade classrooms.

Mary Ann Jacob, a library clerk at the school, said she heard a weird noise over the intercom and called the front desk, at which time she was informed there was a shooting.

Jacob said she yelled out "lockdown" in the library and warned the classroom across the hall. The fourth-grade class of 18 students and four adults in the library took cover. Jacob eventually moved the students into a storage room and locked the door, putting file cabinets in front to protect the students from possible gun fire.

The students were handed crayons and paper to pass the time, and were scared but calm, Jacob said.

"We were afraid he was going to come down the hallway," Jacob said. "We didn't know where he was. We could hear the shots."

As state and local police in Newtown spent Saturday trying to piece together the bloody scene at Sandy Hook Elementary School, residents of the small Connecticut community struggled to understand what happened to their sleepy New England town.

Signs of support for the victims' families were plastered around town in hopes of beginning the healing.

"This is going to be felt here for years," said Brian Haag, who lives near the school.

Iftikhar Ali said he moved his family back to Newtown after living in Canada because the school system was rated one of the best in the state. His daughter Maleeha Ali, a third-grade student at Sandy Hooks, mourned the death of her favorite former teacher, Victoria Soto, who was killed in the rampage.

"She was very nice and I liked it when she played math games with us," Maleeha Ali said. "I used to always go there every morning to talk for a little while with her."

While the tragedy has tightened the already close knit town of 27,500 people, the loss of so many young lives and young mentors like Hochsprung has many wondering how they will move on.

"When you think about how a school recovers, you think about leadership," Jacob said, "And [Hochsprung] was the one who most could have done that."