A Marine charged with helping to kidnap and murder an Iraqi civilian said Monday that government officials violated his basic rights when they interviewed him about the incident — claims military prosecutors denied.

Lance Cpl. Robert B. Pennington, 22, made the allegations as part of an effort to discredit some of the key pieces of evidence against him: statements he gave in which prosecutors say he admits wrongdoing.

Pennington testified at a hearing Monday that when Naval Criminal Investigative Service agents interviewed him after the April 26 death of Hashim Ibrahim Awad, they threatened him with the death penalty and told him it would be a mistake to ask for an attorney.

An agent "said that would be the worst mistake I could make," Pennington said.

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Pennington, of Mukilteo, Wash., was on his third tour in Iraq and part of a squad of seven Marines and a sailor who have been charged with kidnapping the 52-year-old civilian in the rural Iraqi town of Hamdania. The squad dragged him to a roadside hole and killed him, prosecutors allege, then tried to cover up the killing by planting a shovel and a gun by the body to make it look like Awad was an insurgent.

Pennington was the first in the case to testify and then be cross-examined. Three other members of the squad testified previously as they pleaded guilty to lesser charges.

Government prosecutors said Pennington should not be believed, since he lied before. Immediately after the killing, Pennington and the rest of the squad reported that Awad was an insurgent and were justified in shooting him.

The government called two NCIS agents who testified they did not violate Pennington's rights. Both said the Marine did not ask for an attorney, made several amendments to his statement before signing it and said he understood his rights. They also denied threatening him with the death penalty.

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Pennington's defense attorneys have filed a motion seeking to bar the government from using his statements and other potentially incriminating accounts by fellow squad members. The judge was expected to rule on the motion Tuesday.

Also Tuesday, another Marine in the case, Lance Cpl. Jerry E. Shumate Jr., was expected to plead guilty to new charges of aggravated assault and conspiracy to obstruct justice. All original charges, including murder, kidnapping, conspiracy, larceny, assault and housebreaking, would be dismissed in return for him testifying about the incident, according to his lawyer.

Shumate would become the fourth person to take a plea deal in the case.