Atchison went to a second-floor bathroom, where he was "preparing to confront students." Classes were in session at the time. Kassetas said Francisco Fernandez entered the bathroom where Atchison was gearing up. The police chief said Atchison immediately fired his gun, fatally wounding the teen.

Atchison then walked out to the hallway and encountered Casey Jordan Marquez, and he "immediately shot her dead," Kassetas said.