Outsourcing a War

As most of us have realized the biggest military ally in the war in Iraq is not the British Army, but a horde of mercenaries, usually described as "security contractors". Reports have their number at 20,000, about as much as our "allied" troups combined. Now, these guys do what noone else wants to do, guard supply convoys or provide pricy (around $5,000 for a 20 mile trip) but safe passage from the Bagdad Airport to the green zone. They are voluntees, highly paid, and know the risk.
But who controls these guys? If MSNBC is correct, noone. The provisional authority/govenment excempted them from Iraqi law, and it looks like the US military sure won't do anything about them (bad press, plus you'd have to send your own guys into harms way).
And it keeps politicians safe from war crime charges, if they can deny responsiblity for actions of their own military, whatever your outsourced local subcontractor does is surely not something to be blamed on anyone in DC.