So you think that the perp would not find a “softer” target if he knew that there were armed people in the theater.
It’s way too early to guess what this creep would have done.
However, you don’t get a much “softer” target than a dark theatre full of people engrossed in a movie, especially when you first choke them with gas and are yourself dressed in black with body armor on.
Firing randomly, as he did, is easy. First finding your weapon, then finding the dark perp and aiming in the chaos is a tall order and one that would have put more people in danger in the crossfire..
Best thing to do in this situation was to hit the floor between the seats and call 911.