A trainer at the University of Colorado who works with dozens of schools says culture change is happening, but slowly.
In a written statement, Gov. Hickenlooper said deadly violence against officers is having a chilling impact and the state "must come together and say enough is enough."
Matthew Riehl's six-year descent from a budding attorney to a gunman who live-streamed some of his final violent hours had struggled with episodes of mental illness.
The VA document says Riehl was hospitalized at the veterans medical center in Sheridan, Wyoming, in April 2014 after a psychotic episode.
"You know, I'm not here to hurt anybody but yes I do have firearms,” Matthew Riehl can be heard saying before opening fire on police.
University of Wyoming officers called police in Lone Tree, Colorado, in mid-November to warn them about Riehl, suggesting his rants were indicative of mental illness.
Telluride High School was closed Monday as various law enforcement agencies searched the building.
The shooting appears random and there are no indications that it was an act of terror, said Thornton police spokesman Victor Avila.
Experts say just calling 911 may not be enough to survive a gun attack in the workplace.