Other mistake: During the quake, we see the furniture, wall panels, ceiling tile, windowpanes, vertical blinds, etc., in the office fall, shake, or crack. Yet the leaves of a large potted plant do not move at all.
Other mistake: Outside of the office building, Stewart and Remy take shelter under a vehicle, despite falling debris crushing vehicles in their midst.
Chosen answer: Before he put the uniform on, he was a complete nobody, having the respect of no-one. Now that he's in uniform, he demands that people should respect him, and coupled with the powers of Martial Law (where looters can be shot on sight), takes the lack of respect too far and shoots them.
GalahadFairlight