The security vacuum in Iraq was always ripe for exploitation, not just by insurgents. American troops were never deployed in sufficient numbers to ensure security and the onus shifted to private firms to provide guards for hotels, installations and transport. This "second force'' has always carried out its work in a legal no-man's land.
The private security firms are deeply mistrusted by Iraqis who regard them as arrogant trigger-happy guns for hire, mercenaries by any other name. US soldiers can face court martial if accused of unprovoked assaults or over-reaction, though this does not happen often. But the law in relation to private security firms is vague. There are tens of thousands of mercenaries - or private security operators - in Iraq, including British firms as well as American.
The Blackwater case which resulted from the killing of eight Iraqi civilians in Baghdad when shots were fired from a US State Department convoy on Sunday will have reverberations throughout Iraq.
Blackwater has 1,000 employees in Iraq but there are 180,000 security personnel and Iraqis accuse them of behaving as if they are "unaccountable". It is time they were held to account.