At least one witness has pointed to revenge being a possible motive.
"He pointed to us and he said, 'You ruined my life and now I'm going to ruin yours,'" said Alfrancis de Vera, a student at Sparks Middle School.
After shooting Landsberry and two other classmates, the student turned the semi-automatic handgun on himself and was killed. Federal officials tell CBS News the gun was owned by his parents.
"I just heard this bang and I thought it was a joke," said student Adam Ramierez. "Then I saw people running."
The two 12-year-old victims were rushed to local hospitals.
"One was shot through the shoulder. The other shot in the abdomen. Both sustained non life-threatening injuries," said Sparks Police Department Deputy Chief Tom Miller.
Students and their parents remembered Landsberry, a 45-year-old military veteran, Monday night.
"He was tough, but he had a really soft heart," said 14-year-old Jeremy Hannah. "That's why he became a teacher."
Police say Landsberry died trying to intervene and students took to Twitter to praise their fallen teacher.
One student said "Mr. Landsberry was an amazing teacher with a good heart," and another "Landsberry, forever my favorite coach."
Even Sen. Harry Reid chimed in: "Michael Landsberry: Veteran, wonderful math teacher, admired by students, died a hero."
Landsberry leaves behind a wife and two stepdaughters. He served two tours in Afghanistan with the Nevada National Guard. The school will remain closed for the rest of the week.