A Marine's repeated lies hindered the investigation into the killings of 24 Iraqi men, women and children, a military prosecutor said Wednesday in urging a jury to convict.

First Lt. Andrew Grayson "chose to lie" and continued with a pattern of deception, prosecutor Lt. Col. Paul H. Atterbury told the jury of seven officers during closing arguments.

Grayson's court-martial is the first case to come to trial over the killings 2 1/2 years ago.

Grayson says he did nothing wrong. He was not at the scene of the killings on Nov. 19, 2005, but is accused of a telling a sergeant to delete photographs of the dead from his digital camera and laptop computer.

Prosecutors say Grayson also lied five times to investigators before admitting he ordered the photos deleted.

"Gentlemen, why would an otherwise promising officer make a statement like that? The government's argument is that it was to avoid accountability," Atterbury said.

The statements came a day after a judge reduced charges against Grayson, dismissing a charge of obstruction of justice.

The judge, Maj. Brian Kasprzyk, did not explain why he dropped the charge. He told the jury Wednesday shortly before closing arguments that they should not infer anything from his decision.

Grayson still faces two counts of making false official statements, two counts of trying to fraudulently separate from service, and one count of attempt to deceive by making false statements. If convicted on all counts, he faces up to 20 years in prison.

The killings occurred after a roadside bomb killed a Marine and wounded two others.

After the bombing, Staff Sgt. Frank Wuterich and a squad member allegedly shot five men near a car at the scene, investigators said. Wuterich then allegedly ordered his men into several houses, where they cleared rooms with grenades and gunfire, killing the Iraqis, including women and children.

Four enlisted Marines initially were charged with murder in the case and four officers were charged with failing to investigate the deaths. Charges were dropped against five of the Marines but remain against Grayson, Wuterich and Lt. Col. Jeffrey Chessani.

Still to face court-martial are Wuterich, of Meriden, Conn., whose charges include voluntary manslaughter, and Chessani of Rangely, Colo., who has been charged with dereliction of duty and violation of a lawful order on allegations he mishandled the aftermath of the shooting deaths.

Chessani was the battalion commander.