The Washington Post recently claimed that "when [L. Paul] Bremer left his post, he signed an order exempting U.S. contractors such as Blackwater from being prosecuted under Iraqi law." This is a common misconception and it's sad to see a major publication like the Washington Post getting this wrong.
The order in question is Order 17, which stipulates that "Contractors shall be immune from Iraqi legal process with respect to acts performed by them pursuant to the terms and conditions of a Contract or any sub-contract thereto." In other words, contractors getting drunk and causing trouble in their spare time get no immunity. This is quite different from national military forces, which are unequivocally "immune from Iraqi legal process." In this regard, private security contractors are actually more accountable than the US military.