Why didn't Scagnetti shoot Mickey?
When Mickey lead the hostages into Mallory's cell, with a shotgun aimed at them, Scagnetti had several opportunities to shoot Mickey, but instead he just keeps telling him to put his gun down. Any cop with half a brain knows that if he has a gun on someone, and that person has a shotgun pointed at him, that the cop would logically shoot the guy, before the guy could shoot him.
Scagnetti has no problem murdering an unarmed, helpless woman in the hotel, so why does he have moral qualms about shooting Mickey, who is armed with a shotgun?