This is a Picture from the Naval Yard Shooting: Note The...

This is a picture from the Naval Yard shooting:  note the people with their hands up.

The active shooter protocol:  Police response and you:

•  Police will quickly respond to the area in which shots were last heard and attempt to immediately engage/contain the active shooter
•   First arriving officers will not stop to assist the injured, or evacuate personnel
•   Remain calm
•   Do exactly as police tell you
•   Keep your hands empty and visible at all times
•   If you know where the shooter is, quickly tell the officers
•   DO NOT get in the way of officers

Note:  "Keep your hands empty and visible at all times"
Now what would happen if some idiot is wandering around with a weapon who wasn't part of the Law Enforcement effort?