San Diego: A Marine based at California's Camp Pendleton has been charged with murder and dereliction of duty for his suspected role in the killing of a detainee in Fallujah, Iraq.

Sergeant Ryan Weemer on Tuesday became the third person charged in the case, which centres on allegations that a Marine squad shot a group of unarmed captives during heavy fighting in November 2004.

The case came to light when the 25-year-old Weemer applied for a job with the Secret Service protection agency.

Investigators claim Weemer described the killing during a polygraph test that included a question about whether he had participated in a wrongful death.