I am not surprised it happened. American soldiers have committed atrocities in practically every war they have fought in. War is a stressful place and all military/political leaders can due is try to contain it and punish those responsible.
The thing is that the American military is held to an almost impossibly perfect standard, and while that is is a worthy goal, it is idealistic and unreasonable. The Iraqi insurgency commits mass killings every other day of innocents, but if it isn't Americans doing the killings, no one seems to bats an eyelash. Practically every car bomb is reported as a failure of the US Military to prevent it, instead of the blame being put where it belongs, on the shoulders of the insurgents.
I thought this guy at The Times gave a reasonable analysis.
The challenges in Iraq for these young men and women are overwhelming. In the past three years more than half a million American troops have been rotated through the country. They have been fighting a suicidal counter-insurgency in a battle for which they are ill-equipped and ill-trained. While barbarity cannot ever be condoned, it beggars belief to think that in these conditions, with these numbers, outrages will never occur.
You could put half a million Buddhist monks into the mantrap that is Anbar province and I guarantee you’d get an atrocity or two. With most of the painstaking nation building and counter-terrorism efforts of these Americans virtually unnoticed by a critical world, a signal victory such as the al-Zarqawi killing is critical.
How the US responds to the mistakes of its military is the most important thing. The American military punishes its soldiers who commit war crimes, which is the opposite of the behavior of the insurgents who are glorified for attacking civilians on purpose.
