A motion filed by Sgt. Frank Wuterich's attorneys claims that Gen. James Mattis, who initially leveled charges against Wuterich and seven other Marines, was improperly influenced in legal matters by an aide who was involved in the investigation into the shooting, Col. John Ewers.
According to senior defense counsel Haytham Faraj, court martial law prevents someone involved in the investigation from giving advice on legal matters related to the case.
"The process that we're talking about is essential to bringing charges forward," Faraj told ABC News. "The process has to remain pure to ensure that the accused's rights are protected. We believe it was flawed."
Seven other Marines had been charged in connection to the killings and the ensuing alleged cover-up, but charges against six of them were dismissed and the seventh was acquitted.
"We are waiting for a conviction," said A.J. Kadhim, vice president of the American Iraqi Association of North Texas. "What happened in Haditha was incorrect for everybody. We were so sad to see innocent people get killed for no reason. But we do believe in the court system in the United States. If they are innocent, we will go with the law.
"It's a war zone, you know what I mean?... There's no justice in general," he said.
Mattis, a four-star general who is now commander of the U.S. Joint Forces Command, testified Monday that he had already made his decisions about the charges before Ewers came on as an adviser, reported Bob Lawrence of ABC San Diego affiliate KGTV.
When asked by prosecutors if he was ever influenced by anyone in the case, Mattis replied, "No, never."
The hearing will not determine whether or not Wuterich should be criminally prosecuted for the incident in Haditha, but whether the charges were brought against him properly. If the motion succeeds and the judge drops the charges "without prejudice," then the government can start the process over with new charges.
On Nov. 20, 2005, the bodies of 24 Iraqi civilians were wrapped in colorful cloth and lain on the floor of a building in Haditha, Iraq. Some of the bundles were much smaller than others. Those were the children.
The day before, a squad of U.S. Marines had been attacked by a roadside bomb. One Marine was killed in the attack.
The Marines' squad leader, Staff Sgt. Wuterich, and another Marine then fired at a group of nearby Iraqis who were fleeing the scene. They killed five, according to the account Wuterich gave CBS' 60 Minutes in August 2008.
Wuterich said his men came under fire, but didn't know from which direction the shots were coming. Wuterich ordered his men to clear a nearby house and, by his own account, to shoot first and ask questions later, according to the CBS report. His men cracked the door and rolled a grenade in.
"…I remember there may have been women in there, may have been children in there," he said. "My responsibility as a squad leader is to make sure that none of the rest of my guys died ... and at that point we were still on the assault, so no, I don't believe [I should have stopped the attack]."
He went with his troops to the next house.
"We went through that house much the same, prepping the room with grenades, going in there, and eliminating the threat and engaging the targets…There probably wasn't [a threat], now that I look back on it. But there, in that time, yes, I believed there was a threat," he told CBS.
In the end, 24 civilians were dead, including a three-year-old and a two-year-old.
After TIME Magazine broke the story in spring 2006, the military launched two probes into the incident -- one led by former Special Forces commander Maj. Gen. Eldon Bargewell and another by the Naval Criminal Investigative Service, or NCIS.
Bargewell's report claimed Marine Corps commanders in Iraq showed a "willful" failure to investigate the killings, the New York Times reported in 2007.
Mattis told the court Monday that he based his decisions to charge the eight Marines on the results of the NCIS probe. Wuterich was originally charged with murder, but the charge was later reduced to voluntary manslaughter.
In 2008 a judge found that Mattis was unduly influenced by Ewers when charges against Lt. Col. Jeffrey Chessani were dropped without prejudice. Chessani was not involved in the shooting, but was accused of failing to investigate the incident.
In that case the government did not renew the quest for criminal charges and, after facing a Board of Inquiry, Chessani was ordered to be discharged at his current rank, according to the Thomas More Law Center.
When handing down the dismissal of Chessani's charges in 2008, the judge in the case, Col. Steven Folsom, said, "Unlawful command influence is the mortal enemy of military justice," according to The Associated Press.
"In order to restore the public confidence, we need to take it back. We need to turn the clock back," he said.
Lt. Col. David Jones, acting now as judge in the case, is expected to hand down his decision at the end of the week.
If the motion is defeated, Wuterich is scheduled to appear in court in September on charges of voluntary manslaughter, aggravated assault, reckless endangerment, dereliction of duty and obstruction of justice. Wuterich pleaded not guilty.