A Sparks Middle School student, back to camera, cries with family members after being released from Agnes Risley Elementary School Monday Oct. 21, 2013, in Sparks Nev., after a shooting at Sparks Middle School. (AP) - Students at a Nevada middle school were filing off buses and reuniting with friends on the playground after a weeklong vacation when the pop of gunfire shattered the morning calm. Children fled the campus for their lives before the first bell rang. Police said a Sparks Middle School student was the lone gunman who injured two young classmates, killed himself and took the life of an 8th-grade math teacher who tried to stop the rampage. The teacher, former serviceman Michael Landsberry, 45, was being hailed for trying to protect students from a shooting that was witnessed by 20 or 30 children. "We have a lot of heroes today, including our children ... and our fallen hero, an amazing teacher," Washoe County School District Superintendent Pedro Martinez said. Authorities did not provide a motive for the shooting, and it's not known where he got the gun. The 12-year-old wounded students were listed in stable condition. Parents clung to their teary-eyed children at an evacuation center, while the community struggled to make sense of the latest episode of schoolyard violence to rock the nation less than a year after the massacre in Newtown, Conn. "It's not supposed to happen here," said Chanda Landsberry, the slain teacher's sister-in-law. Investigators were still trying to piece together the chain of events that began around 7:15 a.m. Monday, 15 minutes before classes were set to begin for roughly 700 students in the 7th and 8th grades. "As you can imagine, the best description is chaos," Reno Deputy Police Chief Tom Robinson said. It was no shock to family members that Landsberry - a married military veteran with two stepdaughters - would take a bullet. "To hear that he was trying to stop that is not surprising by any means," said Chanda Landsberry. She added his life could be summed up by his love of family, his students and his country. On his school website, Michael Landsberry posted a picture of a brown bear and took on a tough-love tone, telling students, "I have one classroom rule and it is very simple: 'Thou Shall Not Annoy Mr. L.'" "The kids loved him," Chanda Landsberry said. Sparks Mayor Geno Martini said Landsberry served two tours in Afghanistan with the Nevada National Guard and was well known in the school community. "He proudly served his country and was proudly defending the students at his school," he said. The mayor praised the quick response from law officers who arrived at the scene within 3 minutes of the initial 911 calls to find the gunman with a self-inflicted gunshot wound to the head. "They got it under control very quickly and shut down the scene," said Martini, who urged listeners on a local radio station hours after the shooting to be sure all guns in their homes are locked away safely. "I couldn't understand how this kid got a gun," he said. I'm sure his parents didn't give it to him. The middle school will remain closed for the week along with an adjacent elementary school. "We came flying down here to get our kids," said Mike Fiorica, who came to the evacuation center to meet up with his nephew, a Sparks Middle school student. The Washoe County School District, which oversees Sparks Middle School, held a session in the spring in light of the Connecticut tragedy to educate parents on what safety measures the district takes. Associated Press writer Michelle Rindels in Las Vegas and news researcher Rhonda Shafner in New York City contributed to this report.