We know with absolute certainty that armed citizens would have stopped the rampage in its infancy. Gun free zones are free kill zones for mass murderers.
I suppose that doesn't fit the story the left wants told because the presence of the officer, while reported in the second set of MSM reports disappeared later. I am guessing he was a hired security guard. Clubs like that like to have off duty cops as their security guards. Gun free zones aren't "gun free" for police, on or off duty.