The Geneva Convention does cite engagements that are illegal -- mutilation of bodies, deliberate attacks on individuals with high explosives and so forth, but I recall being instructed that if I were to use my Mk19Mod3 grenade launcher or M2 .50 cal in direct fire against enemy troops that I am really only firing at their material assets: Canteens on their hips, their backpacks, etc.
These dead men were guerillas -- terrorists out of uniform. Looks like a perfectly legal gooping of these guys to me.
In the Marine Corps, I knew a Staff Sergeant who told me that he used a TOW missile against a Lebanese militiaman shortly after 241 Marines were killed in the barracks bombing in Lebanon. They were not permitted to fire on a target of opportunity unless it was 'an armed and/or armored vehicle', but they were angrily awaiting some payback.
... Along comes a Lebanese Hizbollah terrorist riding a ten-speed bicycle toting an RPG over his shoulder at a thousand yards away. The TOW crew radioed for permission and then blew him and his bicycle into orbit. This sergeant swore that the bike flew end over end straight up in the air about thirty stories high. Terrorist went in about ten different directions. Poor bastard never knew what hit him.
Sounds about right.
Have you ever been in combat on the receiving end? It'll change your attitude about sympathy for the 'poor' enemy.