The friend shot and killed an off-duty policeman while trying to escape, then killed himself.

NEWYORKER: Hellhole

An Afghan man thought to be an off-duty policeman also died in the incident.

BBC: Cpl David O'Connor, Cpl Channing Day

They were in a fire-fight while on patrol in Helmand province in which an Afghan man, thought to be an off-duty policeman, also died.

BBC: Cpl Channing Day

Davis was convicted for the 1989 murder of an off-duty policeman.

FORBES: The State of Georgia Has Killed Troy Anthony Davis

Afghan officials had said the British patrol had shot dead an off-duty Afghan policeman who was not in uniform but was carrying a weapon as he washed in a stream - mistaking him for an insurgent.

BBC: Cpl David O'Connor, Cpl Channing Day

On 24 October, Marine Cpl David O'Connor, of 40 Commando, and Army medic Cpl Channing Day, of 3 Medical Regiment, were shot in Nahr-e Saraj district of Helmand province in a suspected insider attack by an off-duty Afghan policeman.

BBC: UK soldier killed in Afghanistan 'insider attack'