[Bloody Sam Roberts]

Unless the officer was in the exact location as the shooter, it would be over before they could react.

With such a plan in place, an armed security guard would have been at that locked door when the perp started to smash the glass with the butt of his rifle.

Officer backs off clear of the entrance and when perp enters, officer drops him. Game over.

[Coldwater Creek]

Only in a perfect world!