No one knows why he picked this day, this time, these victims.
It was the first day back from fall break at Sparks Middle School. Students milled about, waiting to hear the morning bell.
Within moments, two 12-year-old students were wounded. A beloved teacher and military veteran lay dead. And the young shooter - armed with his parents' gun - took his own life, silencing any way of understanding what he was thinking.
Before Monday morning, the young gunman seemed like the antithesis of a school shooter.
"He was really a nice kid," schoolmate Amaya Newton told CNN. "He would make you smile when you were having bad day."
But for whatever reason, the boy, whom authorities have not identified, took his parents' handgun to school, a federal law enforcement source said.
"I believe it was because I saw him getting bullied a couple of times, and I think he took out his bullying," Amaya said.
Amaya said she thought the two students at the Nevada school were friends of the shooter.
"It's too early to say whether he was targeting specific people or just going on an indiscriminate shooting spree," Reno police Deputy Chief Tom Robinson said.