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: As the earthquake hits, outside of the movie theatre, a blonde, short-haired woman in an orange shirt and beige pants is running out of the theatre. A second later, she is pummeled by bricks along with two others and collapses to the sidewalk. Then, she is coming out of a doorway a couple of seconds later.
Other mistake: Early in the movie, at the dam when Fred is found drowned in the elevator, there was not enough water trapped in the elevator to drown him.
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