A gunman who allegedly obsessed over the Columbine school massacre before shooting two people dead in a Northern California library has been identified.

Cops released the mugshot for Bradley Scott Sayer, 18, the morning after he is accused of bursting into Butte County Library and opening fire.

The teenager had only just graduated from Chico High School, with a video from the day showing him looking miserable as he got his diploma before shaking his head as he walked off the stage.

Sayer allegedly killed two people at the library late Monday, and also left a child injured.

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