"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.