Zobaie, 51, knows the nature of the men in black masks. He is a former insurgent. Now, as the police chief, he has turned against the insurgency, especially al-Qaeda in Iraq. The U.S. military showcases Fallujah as a model city where U.S. policies are finally paying off and is spending hundreds of millions of dollars in the region to promote the rule of law and a variety of nation-building efforts.

But the security that has been achieved here is fragile, the result of harsh tactics recalling the rule of Saddam Hussein, who was overthrown five years ago. Even as they work alongside U.S. forces, Zobaie's men admit they have beaten and tortured suspects to force confessions and exact revenge.