What stopped Arapahoe shooter?

Where's the national media on this? We're supposed to believe the heavily-armed shooter took a couple of shots and then just decided to kill himself? 

Details somewhat sketchy, but apparently he killed himself when a good guy with a gun showed up.

The Denver Post identifies that person as a deputy sheriff acting as a school resource officer: The quick actions of a deputy sheriff working as the school's resource officer and an unarmed security guard undoubtedly saved lives...They immediately dashed from the cafeteria down a long hallway to the library while yelling for students to get down and get back. "The shooter knew the deputy was coming..."

Townhall.com:  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.

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The kid had what's described as a "large amount" of ammo. 

Imagine if the school had been a "Gun Free Zone."