The Associated Press is reporting that the State Department promised Blackwater bodyguards immunity in its investigation of last month's killing of 17 Iraqi civilians.

"Once you give immunity, you can't take it away," a senior law enforcement official familiar with the investigation told AP.

That means it's possible no criminal charges will be brought, or, if they are, it may take months.

No comment from Blackwater, the State Department, Justice Department or the FBI.

AP writes: Three senior law enforcement officials said all the Blackwater bodyguards involved ? both in the vehicle convoy and in at least two helicopters above ? were given the legal protections as investigators from the Bureau of Diplomatic Security sought to find out what happened. The bureau is an arm of the State Department. The investigative misstep comes in the wake of already-strained relations between the United States and Iraq, which is demanding the right to launch its own prosecution of the Blackwater bodyguards. ...