You kill someone in front of a cop, they aren't bound by some magical code to be forced to risk their life and attempt an arrest on you. There is no rule in which the cop has to be under direct fire in order to shoot either. It's common sense that if people are getting shot, as an officer you defend them, regardless. Cop's keep the peace. Dero shouldn't have worded it in such a harsh manner, however DarkRP can get a bit more then hectic sometimes. There was no real abuse of power, any real disrespect, or neglect of the rules so this is going to be Rejected.
You shoot people, you get shot, that's how it is.