The jury at Bulford Court Martial Centre in Wiltshire heard that the victim, already severely injured by an Apache helicopter after an attack on a local patrol base, was shot at close range with a 9mm pistol by Marine A in a field.
Audio clips of a video showing the killing inadvertently filmed by Marine B on his helmet camera were released in court in November, but the judge blocked the release of the full video evidence to avoid it being used as propaganda.
In the clips, Marine A can be heard shooting the man and then saying: "There you are. Shuffle off this mortal coil. It's nothing you wouldn't do to us."
Marine A was an experienced sergeant at the time of the shooting and will now be sentenced at a later date, but faces a mandatory life sentence.
Presented by Adam Justice