PBS had a documentary about the Blackwater guys a couple of years back. Very interesting. They operate pretty much with no civilian or military oversight (or at least they did at the time) so while they are driving down the Iraqi highways they have tail gunners shooting at any driver they feel is getting too close. But since they have no real oversight, they aren't held to the same standards that our men & women in uniform are. So some of these guys can just be killing random civilians for their own amusement and not be held accountable.
Well since I worked for Blackwater, I will chime in here and say that you are misinformed and your statement is way off base. The men and women here are all former military and heavy on the spec ops end. Well gunners don't just "shoot at any vehicle they feel is getting too close." The use of force is set by the state department and they provide our oversight. Diplomatic security agents head each team. I was a Marine for 12 years and worked in civilian law enforcement as well. Please remove head from ass before speaking about something based on what you heard on CNN or read in the Washington Post. Our whole mission here is security for US personnel and despite how it is depicted on TV, there are no battalions of mercs running around engaging people.