Federal officials and legal experts agree that what the State Department gave to Blackwater guards in Iraq is not immunity from prosecution but rather a promise not to use statements by the employees against them.

The Justice Department says the move by State's diplomatic security investigators complicated the effort to prosecute Blackwater employees. But this may all be academic, given the doubt about whether federal law actually covers their activities in Iraq in the first place.

Justice and State Department officials say Diplomatic Security investigators told the Blackwater guards that they must answer questions, but that anything they said would not be used against them. This is a standard warning in government misconduct investigations, though some legal experts are surprised it was given in a case like this involving potential criminal conduct.

The tactic is an outgrowth of a 1967 U.S. Supreme Court decision. The court said if government employees are told they'll be dismissed if they don't cooperate with an internal investigation, anything they say cannot be used to prosecute them. In other words, the government can't coerce employees into self-incrimination by threatening to fire them. State apparently decided that same protection extends to contractors. And a State Department official today says this procedure has been used routinely by State investigators in Iraq following shooting incidents.

A team of FBI agents was sent to Iraq specifically to work around the immunity problem. Its task was to gather evidence independent of what Blackwater told State's Diplomatic Security investigators. Today, a Justice spokesman says, "Any suggestion that the Blackwater employees in question have been given immunity from federal criminal prosecution is inaccurate. The Justice Department and the FBI continue the criminal investigation of this matter knowing that this investigation involves a number of complex issues."

That's an understatement. Federal law says Americans who commit crimes overseas can be prosecuted if they do it "while employed by or accompanying the Armed Forces." Many legal experts say Blackwater, working under contract to the State Department, doesn't come under that law.

For now, the FBI continues its investigation. Agents have not yet talked to all the Blackwater employees involved, some of whom have returned to the US and others of whom have obtained lawyers.