Under international law, any combatant can be engaged as an enemy. If police fight in a war, they can be shot. However you can't just go around massacring cops if they aren't fighting. >>1775
That's not true. Police in most countries are legally civilians. In common law states, the power of arrest comes from the ancient right to bring an accused criminal before a court. In the US, cops are basically just a privileged class of civilians who get access to cool guns and the ability to get away with murder.