A Royal Marine was found guilty yesterday of murdering an injured Afghan Taliban fighter in September 2011 by a military court martial.

The killer, know only as Marine A, faces mandatory life imprisonment for executing his victim at point-blank range.

Top ranking marine Brigadier Bill Dunham called it a "truly shocking and appalling aberration."

Marine A and at least four colleagues were on patrol in Helmand when they found the seriously injured fighter lying in a field.

He ordered two other marines, labelled Marine B and Marine C, to drag the man into woods before sho0ting him in the chest with a 9mm pistol.

Before executing the stricken man, Marine A said: "There you are. Shuffle off this mortal coil, you c***. It's nothing you wouldn't do to us."

He then turned to Marine B and C and added: "Obviously this doesn't go anywhere, fellas. I just broke the Geneva Convention."

Marine B, who was inadvertantly recording the incident on his helmet camera, replied: Yeah, roger mate."

The murder was only uncovered a year later when police found the recording.

Brigadier Dunham said: "It should not have happened and it should never happen again."

But Marine B and Marine C were acquitted of murder charges and are free to return to service.