AP: Blackwater Guards Given Immunity in Deadly Baghdad Shooting

It's not clear why the Diplomatic Security investigators agreed to give immunity to the bodyguards, or who authorized doing so.

Bureau of Diplomatic Security chief Richard Griffin last week announced his resignation, effective Thursday. Senior State Department officials, speaking on condition of anonymity, have said his departure was directly related to his oversight of Blackwater contractors.

Tyrrell, the Blackwater spokeswoman, said the company was alerted Oct. 2 that FBI would be taking over the investigation from the State Department. She declined further comment.

On Oct. 3, State Department Sean McCormack said the FBI had been called in to assist Diplomatic Security investigators. A day later, he said the FBI had taken over the probe.

"We, internally and in talking with the FBI, had been thinking about the idea of the FBI leading the investigation for a number of different reasons," McCormack told reporters during an Oct. 4 briefing.

Last week, Secretary of State Condoleezza Rice ordered a series of measures to boost government oversight of the private guards who protect American diplomats in Iraq. They include increased monitoring and explicit rules on when and how they can use deadly force.