Why do American Mercenary Companies have Immunity from Prosecution for their War Crimes in the first place?

Security contractors working in Iraq will no longer receive immunity from prosecution in that nation under a deal being brokered by Iraqi and U.S. officials, Iraqi Foreign Minister Hoshyar Zebari said.

Zebari said he briefed Iraqi parliament members about the immunity agreement Tuesday during a closed-door meeting. Officials at the U.S. State Department, which is leading the U.S. side of the negotiations, could not be immediately reached for comment.

The immunity issue was one of the sticking points in talks over a long-term security pact that deals with, among other things, the future of the U.S. military presence in Iraq. Negotiations on the pact continue.

The reported immunity agreement comes more than nine months after an incident in which Iraqi officials allege guards with the Blackwater security firm shot and killed 17 people, including women and children, and wounded 27 at Baghdad's Nusoor Square.

Survivors and victims' family members allege Blackwater guards started shooting without provocation, but Blackwater said armed insurgents attacked its guards.

Blackwater is one of the contractors providing security services for the State Department in Iraq. Under a provision instituted in the early days of the U.S.-led occupation of Iraq, security contractors have had immunity from Iraqi law.

[...]