LaCroix and his team do not wear masks, yet all of the police officers and SWAT agents are, makes zero sense. Plus SWAT agents wouldn't be worried about something like a face mask when dealing with something as serious as a school shooting, face masks make breathing difficult when engaged in vigorous activities like a running fire fight.
Agents are shown using poor trigger discipline. LaCroix and Barnes both have their fingers on their triggers when searching the school, one of the things that is drilled into law enforcement personnel in training is to never walk around with their finger on the trigger. The finger is to remain outside the trigger guard except when firing, or when stationary and facing the possibility of firing, this prevents accidental discharge.
Ira is shown cycling the action on his shotgun at least three different times even though he never fires a single shot.