CAMP PENDLETON -- A Marine accused of killing one of four unarmed detainees during a November 2004 battle for the Iraqi city of Fallujah pleaded not guilty Monday at his arraignment in a base courtroom.

Sgt. Jermaine Nelson faces a Jan. 5 trial before a military jury on one count of unpremeditated murder and multiple counts of dereliction of duty.

Authorities say the killing took place inside a house during the opening hours of the battle for the insurgent-held city.

Nelson's attorney, Capt. Joseph Grimm, indicated to Lt. Col. Jeffrey Meeks, the military judge, that Nelson will assert post-traumatic stress, sleep deprivation and lack of responsibility.

Grimm told Meeks that Nelson was a veteran of two Iraqi deployments, the first coming during the March 2003 invasion in which Nelson took part in the march to Baghdad.

Grimm and Nelson's two other attorneys are trying to suppress statements he made to investigators.

Attorneys for another man accused in the case, Sgt. Ryan Weemer, are trying to suppress statements he made as well. He faces the same charges as Nelson.

The case developed more than two years ago when Weemer told a Secret Service agent during a job interview with that agency that he was aware of unlawful killings during his service in Fallujah.

The man who led the Camp Pendleton squad from the 3rd Battalion, 1st Marine Regiment during the incident, former Marine Sgt. Jose L. Nazario Jr., was tried in U.S. District Court in Riverside earlier this year on charges he caused the deaths of the four detainees and was responsible for shooting two of the men. The bodies of the unidentified men were never found.

A civilian jury that heard Nazario's trial in August acquitted him. Some jurors said it was not their place to decide the guilt or innocence of troops accused of wrongdoing during combat. They also said the lack of physical evidence was a key factor in the not-guilty verdict.

Nazario's trial was the first time a former service member was prosecuted in civilian court under the Military Extraterritorial Judicial Act authorized by Congress eight years ago. A provision of that act allows federal prosecutions of people who are out of the military when accusations arise against them for actions taken during their active-duty years.

Nazario had left the Marine Corps before allegations of the detainee slayings came to light.

A day after his acquittal, Nazario told the North County Times that his most vivid memory of Fallujah was "constant fear."

"We were running out of ammo and we weren't able to clear every house," he said. "We were moving past buildings and structures where we could have been ambushed at any time."

Nelson faces a possible life prison sentence if convicted of unpremeditated murder, the military equivalent of second-degree murder. Under the military justice system, it will be the jury that decides his punishment if he is convicted.

Contact staff writer Mark Walker at (760) 740-3529 or mlwalker@nctimes.com.