Three young children and a teacher were killed Thursday afternoon in a horrific shooting at an elementary school in Bend, Oregon, and a teenage suspect was fatally shot by a good Samaritan who pursued him.

The shooter forced entry into Silver Rail Elementary School by firing through the locked doors around 1 p.m. PT (4 p.m. ET), Bend police said.

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Police arrived within three minutes and learned the suspect had been shot and killed.

Many questions remain about the motive and how the shooter gained access to the long gun used in the attack.

Here's what we know.

Timeline

Police arrived within three minutes of the first call for help.

Deschutes County dispatch received a call at 12:59 p.m. PT from a person in a vehicle saying they were being  shot at multiple times by a person with a long gun,  Bend Police Chief Mike Krantz said at a news conference Thursday evening.

In the ensuing minutes, dispatch received  dozens  of 911 calls reporting that a shooter had entered the K-5 school, he said.

A tone alert was issued at 1 p.m. telling all law enforcement officers to report to a critical incident.

One minute later, the school was directed to go into lockdown.

At 1:02 p.m., the first Bend police officers arrived and moments later learned that a suspect  had been shot by a community member who had seen the suspect enter the school and pursued him into the school and engaged him,  Krantz said.

Officials did not say how far the gunman got into the school, which has more than 400 students and over 40 staff members.

Officers entered the school, confirmed the suspect was dead and began to evacuate it, busing people to a reunification center at a nearby church and providing aid to the victims.

Oregon Gov. Tina Kotek praised the courage of the school's staff members, parents and first responders and the unidentified community member who  heroically intervened to stop further loss of life. 

Multiple people, including children, were injured in a shooting at Silver Rail Elementary School in Bend, Oregon, on Oct. 15, police sa
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