The skill of smoothly reholstering and storing the gun back out of sight need to be practiced just as often as accurate shooting. If you are an armed citizen like Elisjsha Dicken and you just neutralized an armed threat, OR, you didn't get to neutralize the threat yet but you notice that police tactical teams are already on scene, you NEED to immediately reholster and put the gun away right there. By the time you make contact with uniformed responders, your gun is not to be visible.
It sucks, but active shooter and terrorist situations are extreme stress situations. When uniformed responders show up, they tend to assume that ANYBODY armed who is not wearing a uniform is a potential tango. Undercover and plainclothes officers have been blasted by their own uniformed comrades in the past during shooting involved violent arrests. The only time it is safe for anyone to openly brandish a weapon when interacting with uniformed responders is if they are ALSO wearing a uniform that immediately identifies them as an armed professional security guard or an officer of another jurisdiction, county, state department.