The next day, the U.S. Marine Corps opened an investigation.
The suspect's commander, Lieutenant General John Sattler, said in Al-Fallujah that the military is trying to determine the circumstances of the killing. He said the soldier might have acted in self-defense, but added: "We follow the law of armed conflict and we hold ourselves to a high standard of accountability. The facts of this case will be thoroughly pursued to make an informed decision and to protect the rights of all persons involved."
The killing on 13 November, which shocked international and American public opinion, is not the first instance of possible wrongdoing by U.S. forces in Iraq. Nor is it the first time the military has been forced to investigate the behavior of its soldiers during fighting in both Iraq and Afghanistan.
Last summer, U.S. credibility suffered a major blow after news broke that U.S. soldiers had abused Iraqi detainees at the Abu Ghurayb prison near Baghdad. Other prisoner-abuse scandals later surfaced in Afghanistan.
In all these cases, the U.S. military has appeared to act quickly to probe alleged criminal behavior. But whether the military's justice system has worked effectively depends on who is asked.
Steven Welsh, an analyst at the Washington-based Center for Defense Information, told RFE/RL that compared to most other countries, the American military has a very good internal justice system.
"As an institution, the U.S. military has arguably the most advanced system of military justice in the world, and it's one of its great assets, which I think also goes hand in hand with being a superpower and having such a strong military, because rule of law dovetails with military discipline and respect for the command structure," Welsh said.
Reed Brody, a lawyer for the advocacy group Human Rights Watch, agreed that the Pentagon appears to be assertive in prosecuting wrongdoing by its soldiers. But he told RFE/RL that it took the torture and abuse scandal at Abu Ghurayb prison to spur American officials into action.
"For individual soldiers who are alleged to have committed abuses, the military was very slow to respond in Afghanistan and Iraq," Brody said. "There was almost no accountability despite a growing number of alleged abuses. After Abu Ghurayb happened, the military justice system was all over the abuses."
Brody also said he believes U.S. military investigations are too limited.
For example, he said he believes the soldiers charged in the Abu Ghurayb abuses would not have acted as they did unless they felt it was what their commanders wanted.
Brody said he believes the ultimate blame lies with senior officials in the administration of U.S. President George W. Bush.
He said they include Defense Secretary Donald Rumsfeld as well as Attorney General John Ashcroft, whose office suggested that the Geneva Conventions may not apply in an unconventional war against guerrilla forces.
One of the soldiers charged in the Abu Ghurayb case is Private Lynndie England, who appears in photographs of some of the episodes of abuse. Brody said that England is as much a victim as she is a suspected victimizer.
"Let's remember, it wasn't Lynndie England who cast aside the Geneva Convention," Brody said. "It wasn't Lynndie England who approved the use of illegal interrogation tactics that violate the Geneva Convention -- things like the use of unmuzzled guard dogs on prisoners. It wasn't Lynndie England who advised the president of the United States that he could get away with torture in the context of the fight against terrorism."
However, according to Welsh, the U.S. military's justice system has numerous positive aspects that are absent in other militaries, mainly because the civilian system from which it is derived is based on strong democratic principles.
Welsh said that a society's legal discipline usually parallels overall discipline in its army.
As an example, Welsh points to the many atrocities attributed to Russian troops in Chechnya, and the reported hazing of Russian military conscripts by fellow soldiers.
"If you look at countries that do not have as strong a sense of rule of law, whether generally or in their militaries, they are also not as effective as the U.S. military, I would argue," Welsh said. "An example -- you know, the Russian quagmire in Chechnya. It's not only how they treat the Chechens, but also how they treat their comrades."
Welsh said it is difficult to rank the U.S. military's internal justice system with that of other Western countries' militaries, because they do not deploy troops as often. But Welsh believes that despite the recent problems, legal discipline in the U.S. military is among the best in the world.