About 500-600 suspected terrorists arrested are in Baghdad each month, many of them caught in the act. But many of these guys get released for "lack of evidence" (even when they were captured, often wounded, after a firefight with American or Iraqi troops). This is hurting morale among American and Iraqi troops, and causing a decline in tips from Iraqi civilians (who see the bad guy out on the street, not long after his arrests, and looking who whoever turned him in.)
Getting a criminal courts system operating in Iraq is proving to be dangerous for American troops, as well as all Iraqis involved. In the past, under Saddam, evidence was manufactured as needed, and prosecutors were accustomed to getting overwhelming cases. But now, much less evidence is available, and prosecutors are often reluctant to prosecute, and judges reluctant to convict. Moreover, the terrorists have threatened and killed prosecutors and judges, making it likely that the a real bad guy, who has lots of murderous friends, can get off simply by having his buddies threaten the court officials. The advice coming from Washington is for American troops to gather more evidence and build more compelling cases. The troops are protesting that the problem lies with the Iraqi courts, and that soldiers should not be forced to operate as police detectives. Eventually, the Iraqis have to deal with their own criminals, and as long as American soldiers have to do it, they are not going to play cops and robbers.