On December 13, 2013, 18-year-old Arapahoe High School student Karl Pierson entered his school armed with a shotgun, a machete, and molotov cocktails intending on killing his former debate coach and possibly others. After firing three shots down a hallway and injuring one of his classmates, Pierson killed himself in a classroom. Today it was revealed why he did this: a "good guy" with a gun had him cornered.

Fox News reports:

When an armed school resource officer entered the room, Pierson believed he was cornered and turned his gun on himself, Robinson said. The entire attack lasted approximately 80 seconds and was captured by security cameras.

Wow.

A janitor informed Pierson's former debate coach to flee the school after he saw Pierson was armed with a gun, likely saving his life.

Investigators have said that they believe Pierson was planning a large-scale attack at the school due to the amount of ammunition he was caring. Claire Davis, the student wounded in the attack, remains in a coma.

Good guys with guns save lives. I shudder to think what would have happened had the resource officer not intervened.