A government prosecutor on Wednesday portrayed a Marine Corps officer facing demotion as a negligent, substandard commander for not investigating the killing of 24 Iraqi men, women and children by Marines under his command.

A defense attorney, however, countered that Lt. Col. Jeffrey Chessani was a brilliant leader who took the fall amid political pressure fueled by inaccurate media reports of what was a chaotic firefight with insurgents _ not a war crime.

The conflicting portraits emerged during opening statements to a three-member military panel that will determine if Chessani should be demoted in retirement for dereliction of duty, a move his civilian attorney says could cost Chessani and his wife a half-million dollars in benefits. The couple is expecting their seventh child.

Lt. Col. Paul Atterbury, a government attorney, told the panel the shootings occurred after an improvised bomb killed one Marine and injured two others while they were on patrol.

In the two hours that followed, a squad of Marines shot five men in a car near the explosion, killed a runner on a ridgetop then swept south into a residential area, killing 18 more civilians in three homes, Atterbury said.

Among the dead were nine women and two children _ deaths that eventually led to $38,000 in condolence payments from the U.S. military.

Chessani didn't visit the scene of the Nov. 19, 2005 shootings until the next day and resisted an investigation even after an initial inspection found no evidence of insurgent activity and after Haditha leaders met with Marines and complained of war crimes, Atterbury said.

In addition, Chessani's reports to his superiors were inaccurate and incomplete, he said.

A full investigation did not begin until January 2006 when a Time magazine reporter inquired.

"What's tragic about the events of the 19th of November is the loss of life," Atterbury said. "How did they die? How did we wind up with more loss of life?"

Chessani had been charged with dereliction of duty for failing to investigate the killings and was relieved of his command in 2006. However, a judge at Camp Pendleton dismissed the charges because of improper contact between a general overseeing the case and an investigator.

The Marines announced in April they would not pursue further criminal charges and referred the case to the administrative panel.

In his opening statement, Chessani's military attorney Lt. Col. Jon Shelburne refuted the government's case and portrayed the incident as part of a complex and coordinated attack on U.S. forces along a 10-mile stretch south of Haditha.