You should elaborate, because if this is the sentence you want, it's no different: Cops can kill at will if they have reason to believe that the other will kill.
They can kill when they have a reasonable basis for assuming they are facing an imminent threat to their lives or addressing a threat to public safety (but NOT to prevent criminal activity that isn't life threatening). That isn't the same thing as a license to kill, and they are accountable for charges like murder when they don't meet a "reasonable officer on the scene" standard. I don't consider that to be "at will" (likened to "at will employment") so much as "at their discretion."
