What we know about teen gunman who police say opened fire at Bend, Oregon school

The 16-year-old gunman who opened fire inside a special needs classroom at Silver Rail Elementary School, killing three boys and a teacher was a former student at the Bend, Oregon school, investigators revealed Friday.

Bend Police Chief Mike Krantz identified the shooter Friday as Griffin John II, a Bend resident. The teenager made his way into the school Thursday afternoon with a Maverick 88 12-gauge pump-action shotgun and opened fire in the classroom after he shot at a truck outside of the school, Krantz told reporters at a news conference on Friday.

The chief did not immediately disclose how the shooter obtained the weapon.

"Currently, the origin of that possession is what we're working on," he said.

Preliminary information indicated the shotgun was believed to have been purchased by his mother, multiple sources told ABC News. 

Krantz said a motive hadn't been immediately determined.

The police chief said the suspect was not currently enrolled in the school district but had previously attended Silver Rail.

Bend-La Pine Schools Superintendent Steven Cook told reporters the shooter had been a special needs student during his time at the school.

Krantz said that search warrants were executed at the shooter's home and investigators are still combing through evidence and interviews.

"I think that's one of the most challenging parts of these types of investigations and cases is determining the why and the motives, and that that is part of the current very active, as I said, open investigation that we're working on," Krantz said.

"And it ... will require substantial investigative time to continue that. But that is the answer we're seeking as well. And as I've said before, we may never get that full answer, but we want it," he added.

The shooting began unfolding around 1 p.m. PT, when the teen threw the shotgun over a fence outside the school and then scaled it, Krantz said. A person in a truck that was nearby observed the shooter and verbally engaged the shooter, according to the chief.

The shooter fired at the truck, striking it at least three times, before he made his way into school, according to the chief.

The teenager shot through a door and made his way into a classroom before opening fire, Krantz said.

Krantz said that the shooter fired at least 15 rounds inside the classroom.

An unidentified teacher threw a phone at the suspect, tackled him and attempted to disarm him, according to the chief.

Another bystander, identified by his family as Kaylub Giamanco, saw the shooter enter the school while he was driving by, Krantz said.

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He pursued the shooter and engaged him, fatally shooting him, Krantz said.

Giamanco has two daughters who attend the school and a concealed carry permit his family said.

Three boys, whose ages were 5, 8 and 11, were killed along with a teacher, Megan Lambert, 25, of Bend. The 5-year-old was identified Friday as Rhoam Summer.

An unidentified 7-year-old girl and Becky Drury, a 54-year-old teacher, were hospitalized with injuries, Krantz said.

The girl was in serious but stable condition, and Drury was being treated for serious but non-life-threatening injuries as of Friday afternoon, according to the chief.

Police are still going through the school but they said that the shooter had approximately 44 remaining rounds of ammunition on his person and in his backpack.