FALLUJA, Iraq (CNN) — The U.S. military is investigating whether a Marine shot dead an unarmed, wounded insurgent during the battle for Falluja in an incident captured on videotape by a pool reporter.

The man was shot in the head at close range Saturday by a Marine who found him among a group of wounded men. The wounded men were found in a mosque that Marines said had been the source of small-arms and rocket-propelled grenade fire the previous day.

Marine shoots a unarmed, wounded insurgent dead