Pfc. John J. Jodka III, 20, entered the pleas through his lawyer, Joseph Casas, after telling the judge at his court-martial that he understood his rights.
Jodka was one of seven Marines and a Navy corpsman initially charged with murder, kidnapping, conspiracy, assault and housebreaking in the killing of 52-year-old Hashim Ibrahim Awad in the Iraqi town of Hamdania.
Jodka — the squad's youngest and lowest-ranked member — was among five Marines who shot at Awad while others stood by then helped cover up the killing, the government charge sheets allege.
"The interest of justice and the best interests of my client will be served by this plea," Casas told the San Diego Union-Tribune before Thursday's hearing. Neither Casas nor Jodka's father would say whether the Marine would have to testify against his co-defendants as part of the deal.
"I'm very disgusted that the case even exists and that (Navy Petty Officer 3rd Class Melson J. Bacos and Jodka) have rolled over on their former brothers, and I emphasize 'their former brothers,'" Terry Pennington of Hawaii, father of Lance Cpl. Robert B. Pennington, told the Union-Tribune. "It angers me totally."
Navy corpsman Bacos pleaded guilty earlier this month to kidnapping and conspiracy.
"He was trained to follow his leaders and do as they commanded without questioning," said Jodka's grandfather, Joe Snodgrass, 71. "He was trying to be the best Marine possible."
He said his grandson had paid for any wrongdoing: Jodka had been locked in the brig since May and his flak jacket had come back peppered with bullet holes from when he had been shot at on patrol.
At his court-martial, Bacos testified that he and the Marines were searching for a known insurgent who had been captured three times and released. The group approached a house where the insurgent was believed to be hiding, but when someone inside woke up, the Marines instead went to another home and grabbed Awad, Bacos said.
The squad took Awad to a roadside hole and shot him before planting a shovel and AK-47 to make it appear he was an insurgent planting a bomb, he said.
Bacos was sentenced to a year's confinement; murder and other charges were dropped.
Former Army prosecutor Tom Umberg said other Marines in the case might follow Bacos' and Jodka's lead and negotiate pleas.
"As the government's evidence gets stronger, the defendants start to look around," Umberg said.
But he acknowledged that deciding to make a deal would be difficult.
"You are trained from day one to support your buddy, and also taught that there are certain values as a soldier or Marine you are fighting to uphold," he said. "The resolution for a young man can be heart-wrenching."
Five other Marines face courts-martial. A decision has not yet been announced on whether squad leader Sgt. Lawrence G. Hutchins will be referred to a court-martial.