when Jeremy Scahill, who wrote a book on the topic
was interviewed on CBC radio a few months back - he said there are
at least 100,000 security contractors in Iraq (dont know how many are blackwater) but under the existing US agreement with the govt of Iraq
they are immune from prosecution in IRaq. (also since they are not military they are not bound by a military code of conduct.)
Scahill was in New Orleans, shortly after Katrina hit, and saw a bunch of armed guys getting out of a vehicle with no plates, and asked a police officer who they were - apparently they were Blackwater guys -
help people perhaps? no provide security against looters.