A third US marine has been charged with murdering a prisoner during fierce fighting in the Iraqi town of Falluja four years ago.
Sergeant Ryan Weemer, 25, was charged with murder and dereliction of duty over the November 9, 2004 incident.
The case centres on allegations that a marine squad shot a group of unarmed captives.
Newspaper reports have said as many as eight fighters were shot dead after being captured.
Under military law, the killing of a captured enemy combatant who does not pose a threat is treated as murder.
Weemer was a rifleman in a four-man team when ground forces entered Falluja and faced heavy fighting, often engaging in hand-to-hand combat.
The authorities say his involvement came to light during a lie-detector test when he was applying for a job with the Secret Service protective agency after he completed active duty in the military.
Investigators say Weemer described the killing during a polygraph lie-detector test that included a question about whether he had participated in a wrongful death.
Weemer, who remained a marine reserve, was reactivated this week, paving the way for him to be court-martialled.
Another marine from Weemer's unit, Sergeant Jermaine Nelson, was charged with murder last year in connection with the death of a detainee.
A third soldier, Jose Nazario, is being tried in civilian courts in California on manslaughter charges in connection with the shooting deaths of two Iraqi prisoners.
Nazario, who denies the charges, is awaiting trial.