If a soldier kills a civilian, or two, it is lawful combat.
If a civilian kills a soldier, it is unlawful combat.
This is called asymmetric warfare.
Bush said he would not distinguish between Al Qaida and those who harbored Al Qaida. The Taliban, who governed Afghanistan, harbored al Qaida. So we declared war on Afghanistan. (Didn't we?)
Taliban prisoners are prisoners of war. If we make no distinction, Al Qaida prisoners are prisoners of war as well.
During the revolutionary war, most of the naval forces were privateers. This afforded POW status if captured.
Were the Blackwater contractors lawful or unlawful enemy combatants from the point of view of the people of Falluja?