Because they are empowered by a corrupt and power hungry government. The rules don't apply to them by design which is utter bullshit. It'll get to the point where the common citizenry deals with it one way or the other. If something like this happened in a CCW state by plain clothes cops the cops might not be here today. Just imagine walking around a corner and seeing some nut case firing away at some unarmed guy and watching bystanders getting hit.