The soldiers first took some of the men into custody because they were using two women and a toddler as human shields. They shot three of the men after the women and child were safe and say the men attacked them.

"The ROE (rule of engagement) was to kill all military age males on Objective Murray," Staff Sgt. Raymond L. Girouard told investigators, referring to the target by its code name.

In Fallujah, the Army prohibited military age males from fleeing the city during the late 2004 offensive. The Army also had orders to shoot any men between the ages of 15 and 50 seen on the street, regardless of wether the men were armed or not. This policy was also reported on by the NY Times during the April 2004 offensive on Fallujah. According to the Times, at least one battallion had 'orders to shoot any male of military age on the streets after dark, armed or not.'

It is very common policy of the US Military to round up all military age males ('MAMs' in the military lingo) in insurgent hotbeds and interrogate them. One PBS reporter describes his reaction to such an event.

I marvel - and sometimes cringe - at the Marines and their strenuous daily efforts to impose rigid American paradigms on this shattered and foreign city and country. A sniper shoots at Marines returning to the firm base from a four-hour patrol, as happened a few days ago. No one sees him, so the Marines round up all the MAMs - military-age males - in the vicinity of the shooting, cuff them, and then interrogate them through a non-Iraqi translator with a loose grasp of English, and whose heavily accented Arabic locals must strain to understand. The grunts treat the "PUCs" - persons under control - rudely and roughly, wrestling them to the ground and cursing them, but they don't hit the men. I feel as if I am watching a bunch of teenagers executing an arrest after watching a season of Cops or Starsky and Hutch reruns. It seems absurd and counterproductive, and such behavior appears to me to bruise Iraqi hearts and minds, not heal them.

Many times, innocent MAMs who are rounded up in mass sweeps may be held as long term detainees. Indeed, according to the Taguba Report about 60% of the detainees held in Abu Ghraib prison during the time the abuses there happened likely hade nothing to do with the insurgency. It is easy to imagine that large numbers of Sunni Arab males in Iraq may have been tortured at one point or another by US forces. Such a policy amounts to collective punishment and probably fuels the insurgency a great deal.

Also, This article by Stan Koff suggests that the practice of treating all young adult men as potential hostiles goes back to Vietnam and is now being seen in Iraq.