The scenario you portray is very worthy of note. In an active shooter situation, lots of people will be running, some may even be armed and attempt to stop the shooter. At this point proper ID and shot placement become more than paramount, but... It is no longer just shot placement, it is also timing too. Why timing? Because you must make sure you dont catch someone running through your field of fire. A 9mm+p or a 357 may have the energy to pass through the assailant and strike an innocent, and regardless of legal consequence, one may feel the emotional responsibility for many moons. Knowing your target (clear ID), and knowing whats behind it are paramount, knowing the strength and capabilities of your firearm are included in this factor. An active shooter scenario in a crowded environment is not the time to exhaust a 16 round mag in a frenzied attempt to land a round. It becomes an exercise in tactical patience, where ones nerves could be put to the extreme limits, and still need to remain focused on that single, well placed, well timed shot on the clearly identified target. ~ In this case, offender was wearing body armor, and the room being filled with tear/cs gas, indeed a worst case scenario.