The teen is accused of killing three children and a teacher at Silver Rail Elementary School in Bend and critically injuring two others.

A 16-year-old boy shot dead three children and a teacher at Silver Rail Elementary School in Bend, Oregon, on October 15. Police named him Friday as Griffin J. John II, a former student at the school. He was shot dead at the scene by a man who was passing by. Two senior law enforcement officials told NBC News that the boy’s mother bought the shotgun he used around his birthday in August. Police have not said why he did it.

WHAT HAPPENED AT THE SCHOOL

Bend Police Chief Mike Krantz gave the timeline at a news conference on Friday. The boy walked up to the school fence, threw a shotgun over it, and climbed after it. A man driving past in a pickup truck stopped near him. The boy fired at the truck at least three times. The driver got away and called 911.

The boy then shot out the glass panes of a set of double doors and went in. NBC News said it happened at about 1 p.m. local time. He went straight into the classroom on the left of the doors and opened fire. Krantz said every victim was shot in that room. It was a special needs classroom, and Bend-La Pine Schools Superintendent Steven Cook said the boy had been a special needs pupil at the school.

Police said he fired up to 15 rounds, using birdshot, buckshot and slugs. A further 44 rounds were found at the scene. Officers got to the school within minutes of the first calls.

THE TEACHER AND THE MAN WHO STOPPED HIM

Krantz said a teacher fought the boy for the gun. According to CBS News, she threw her phone at him, then tackled him. She was not hurt. Krantz said she “almost certainly helped prevent more bloodshed”.

The man who stopped the boy is Kaylub Giamanco, 36, according to his family. He has two daughters at the school. He saw the shooting at the truck and drove into the school car park. He took a .40-calibre pistol, which he owned legally, from his car and went in. Krantz said he heard shots and saw the teacher struggling with the boy. He then went to the classroom and fired, hitting the boy several times.

Krantz called the actions of both the teacher and Giamanco heroic. In a statement, Giamanco’s family said he is not looking for praise and wants to thank first responders, school staff and the community.

THE VICTIMS

The children who died were aged 5, 8 and 11. Police and the family named the youngest as Rhoam Summer. The family said in a statement that they feel “broken and lost”, NBC News said. The teacher who died was Meghan Lambert, 25. The families of the other two children have asked that their names are not made public.

A 7-year-old girl and a 54-year-old teacher were also hurt. Krantz said the girl was in a serious but stable condition at Oregon Health & Science University in Portland. The teacher’s injuries were serious but not life-threatening, and she was being treated at St. Charles Medical Center. At a vigil on Friday, Bend Mayor Melanie Kebler said no words could describe the loss.

THE INVESTIGATION

Police have not named a motive. Officers searched the boy’s home on Friday and are still examining the scene. NBC News said his mother has helped police so far.

CBS News said investigators are going through his computer, phone, social media and search history. They want to know whether he had a fixation on violence, including earlier mass shootings. Its sources stressed that the inquiry is at an early stage.