A horrifying shooting at an elementary school in Oregon has left three children and a teacher dead after a 16-year-old gunman forced his way into the building before being fatally shot by a community member, authorities say.

The attack unfolded Thursday, October 15, at Silver Rail Elementary School in Bend, Oregon. Police said the three children killed were just 5, 8 and 11 years old. A teacher was also killed, while a 7-year-old child and another teacher were taken to the hospital in critical condition.

According to Bend Police Chief Mike Krantz, emergency dispatchers received the first call shortly before 1 p.m. from someone who reported being fired upon by a person carrying a long gun outside the school.

The teenage suspect then allegedly gained entry to the school by firing at locked doors. Police said officers reached the campus within minutes, but by the time they entered, the gunman had already been shot by a community member who witnessed him enter the building and followed him inside.

Authorities have not publicly identified the victims or the 16-year-old suspect. Investigators also have not established a motive or confirmed whether the teenager had any connection to the school. The Associated Press reported that the weapon used was a pump-action shotgun that had been legally purchased by the suspect’s mother.

Oregon Governor Tina Kotek praised the unidentified bystander for intervening, saying the person’s actions helped prevent further loss of life.

Students and staff were evacuated and taken to a nearby church, where families were reunited. Bend-La Pine Schools subsequently canceled classes, athletic events and other activities for Friday as the community mourns the victims.

The FBI and other law-enforcement agencies are assisting local authorities as investigators work to determine what led to the deadly attack.