IMPEACH BUSH

SAN DIEGO, Calif. - Up to 10 U.S. Marines are under investigation for the deaths of eight Iraqi prisoners during the November 2004 battle for Fallujah, marking the third war crimes probe of Marines at California's Camp Pendleton, a government spokesman said Thursday.

Ed Buice, a spokesman for the Naval Criminal Investigative Service, said he could not disclose details of the inquiry at the U.S. Marine Corps base.

But he said none of the Marines under investigation are being held in detention.

Nat Helms, a Vietnam veteran who has written a book about the Marine Corps' battle for Fallujah in Iraq's Anbar province, provided an account of the deaths on his Web site — defendourmarines.com — writing that eight Iraqi prisoners were executed.

According to Helms, Marines held eight unarmed Iraqi men in a house during the battle and executed them after receiving orders to move to a new location.

Any physical evidence in the case was apparently destroyed when the building in which the killings allegedly occurred was leveled by U.S. airstrikes.

Navy officials confirm that the allegations arose when a former Marine corporal was being interviewed for a job with the Secret Service and was asked during a polygraph test if he had ever taken part in an unjustified killing. He didn't get the job.

Navy officials tell NBC News that some of the Marines apparently involved in the alleged killings "are talking."

Another embarrassment?
The allegation is another embarrassment for the U.S. military fighting in Iraq and Camp Pendleton, one the Marine Corps' largest installations in the United States.

In June 2006, seven Marines and a U.S. Navy corpsman were charged in the April 2006 killing of a 52-year-old grandfather in Hamdania, Iraq.

According to testimony, the man was kidnapped from his bed and killed in a scenario planned to make his death look like he was planting a bomb.

All but three of the troops have pleaded guilty to reduced charges, while the remaining three Marines pleaded innocent to charges including kidnapping and murder and are awaiting court martial.

Platoon under fire
In December 2006, eight Marines from the same platoon being investigated in the Fallujah killings were charged in the November 2005 killings of 24 residents of Haditha, Iraq.

Four officers face charges for failing to investigate and accurately report the Haditha killings and three Marines face murder charges. Charges against a fourth Marine were dismissed in exchange for testimony.

The latest investigation began after a Marine admitted during a polygraph test for a job with the U.S. Secret Service that he participated in a wrongful death, according to Helms.

Helms says Corp. Ryan Weemer told him that after Marines captured the eight Iraqis, they received a radio order to move out. When asked what to do with the prisoners, a radio operator asked "Are they still alive?" The Marines took that as an order to execute the Iraqis and shot them to death, Helms says.

According to Helms, insurgents in Fallujah would run from firefights without weapons and rearm themselves at new locations because they knew Marines were barred from shooting the unarmed.

NBC News' Jim Miklaszewski and Reuters contributed to this report.