A central Oregon elementary school became a crime scene in minutes Thursday afternoon after a 16-year-old gunman shot his way through locked doors and opened fire inside, killing three children and a teacher before a bystander ran in after him and shot him dead.

Deschutes County dispatchers got the first call just before 1 p.m. Thursday from a driver who said someone with a long gun had fired at them repeatedly on the street. Within moments, dozens more 911 calls poured in reporting a shooter inside Silver Rail Elementary School in Bend, according to NBC News. Police say the teenager forced his way into the K-5 school by firing through its locked doors.

Officers arrived within about three minutes of the first call and found the suspect already dead, shot by a community member who had seen him enter the building, followed him inside and confronted him, according to CBS News. Four victims were found dead inside: three children, ages 5, 8 and 11, and a teacher. A 7-year-old student and a 54-year-old teacher were rushed to St. Charles Medical Center in critical condition.

"They're All Our Babies"

Bend Police Chief Mike Krantz said officers had completed active-shooter training at a local high school just two months earlier. "Unfortunately, this is something we train for on a regular basis, and we must," he said, according to NBC News's rolling coverage of the shooting. Investigators have not disclosed a motive or said whether the teenager, a Bend resident, had any connection to the school. Law enforcement sources told NBC News the gun was a shotgun his mother had purchased for him around his birthday in August; officials have not detailed how the purchase or the weapon's possession were handled under Oregon's firearms laws.

NO COMMUNITY SHOULD HAVE TO DO WHAT WE ARE DOING RIGHT NOW.

That was how Bend-La Pine Schools Superintendent Steven Cook described the moment, per CBS News. Gov. Tina Kotek credited the unnamed bystander with "heroically" cutting the attack short and said the state "stands ready to support" the community. Bend Mayor Melanie Kebler called it a painful day for a city where, she said, schools should be places where kids feel safe.

Students and staff were evacuated and bused to a nearby church to be reunited with families. Hundreds gathered Thursday night for a vigil at a town park, and Oregon state lawmakers, including Rep. Janelle Bynum, attended, according to local station KTVZ. The FBI and ATF are assisting Bend police and Oregon State Police with the investigation, which officials say will take time to complete. Police said a heavy law enforcement presence will remain posted at the school for several days.

Every school in the Bend-La Pine district canceled classes and athletic events Friday, and the district has set up crisis counseling sessions for students and staff. The names of the victims had not been publicly released as of Friday morning, though police said families had been notified. According to the K-12 School Shooting Database cited by CBS News, Thursday's attack was at least the 149th shooting incident at a U.S. K-12 school so far this year.