Lillian Hannah Jolly-Summer/Swan Sheridan/Handout/AP via CNN Newsource

By Eduardo Cuevas, Alaa Elassar, John Miller, Ray Sanchez

(CNN) - Students in this Oregon community won't be returning to classes on Monday as they continue to mourn three classmates and a teacher killed in the United States' latest school shooting, the motive of which is still unknown.

Officials in Bend, Oregon, are investigating what led a 16-year-old former student of Silver Rail Elementary School to return to the school and open fire inside a special needs classroom on Thursday. Teacher Megan Lambert was killed along with students 5-year-old Rhoam Summer and two others, aged 8 and 11, police said.

 We hold each of them and their families and their loved ones close in our hearts as we mourn together as one community,  Bend-La Pine Superintendent Steve Cook said in a video posted Sunday.  Our responsibilities to care for one another will continue well beyond these first days. 

The shooting stopped when another teacher intervened to tackle the suspect before a good Samaritan - who saw the gunman enter the school and trailed him - fatally shot him, police said.

While the assailant will never face charges, it's unclear whether the juvenile's mother - who reportedly purchased the gun - will face charges similar to those against parents of school shooters in Georgia and Michigan.

Here's what we know about the Silver Rail Elementary shooting, the 36th in the United States this year on K-12 school grounds, according to CNN's analysis of multiple databases, including the Gun Violence Archive.

Where the investigation stands

Law enforcement officials are still looking to understand why the gunman, identified as Griffin J. John II, forced his way into his former elementary school, opening fire into the mixed-age special needs classroom. He previously attended special needs classes at Silver Rail Elementary, officials said, but they couldn't confirm whether he had been a student in that specific classroom.

Investigators on Thursday interviewed the shooter's parents, who were cooperative with officials, a senior law enf
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