More: U.S. soldiers did not find any bullets that came from AK-47 assault rifles or BKC machine guns used by Iraqi policemen and soldiers. They found evidence of ammunition used in American-made weapons, including M4 rifle 5.56mm brass casings, M240B machine gun 7.62mm casings, M203 40mm grenade launcher casings, and stun-grenade dunnage, or packing.

At least two cars, a black four-door taxi and a blue Volkswagen sedan, had their back windshields shot out, but their front windshields were intact, indicating they were shot while driving away from the square, according to the photos and soldiers

An Iraqi colonel walked up to Tarsa and described the Blackwater shooters as men in "tan uniforms, black helmets, and that flag," pointing at the U.S. flag on Tarsa's sleeve.

Their actions underscore the long-standing tensions between the U.S. military and private security companies -- and the military's concerns that such shootings could undermine U.S. efforts to stabilize Iraq.