Police say the suspect was armed with about 44 more rounds of shotgun ammunition when he was stopped. He fired as many as 15 rounds in the class.

"To the people who showed courage in the face of such violence, and intervened to prevent this tragedy from being any worse, we owe you a debt of gratitude," Bend Police Chief Mike Krantz said on Friday.

Police offered more information on the attack at at a news conference on Friday, where they identified two of the four victims. They include five-year-old Rhoam Summer and 25-year-old teacher Meghan Lambert.

The families of the two other students who were killed, an eight-year-old and 11-year-old, did not wish to have them publicly identified yet, police said.

Two others were injured in the attack. Another teacher, a 54-year-old, was still being treated at hospital, and a seven-year-old student, who was in serious but stable condition.

Krantz said the heroic actions of both the teacher and the father who ran inside the school saved lives.

He said the teacher who wrestled with the gunman was not hurt but "almost certainly helped prevent more bloodshed".

He identified the suspect as 16-year-old Griffin J. John II, who previously attended the school and was a special educational needs student there.

A search warrant has been executed at the suspect's home and a search is ongoing, the police chief said.

Police believe the suspect travelled to the elementary school on foot, but police are still investigating his exact movements and how he acquired the gun. A motive is also not clear.