What do you do when someone starts shooting? Ignore the anti-gun slant, this is posted for consideration of tactics only. In this case detectives reviewing video had to rule out anyone who had a gun in their hand as a suspect. If police make entry to stop the shooter they will do the same thing as they clear the building.
http://www.denverpost.com/2017/11/02...mart-shooting/
http://www.latimes.com/nation/la-na-...103-story.html