Testifying before Congress last week, Secretary of State Condoleezza Rice said there's a hole in U.S. law -- she kept calling it a "lacuna" -- that prevents independent contractors like Blackwater from being prosecuted in the United States for crimes committed in Iraq. "We believe there is a lacuna and it needs to be filled," she said.

What Rice didn't say: State Department officials investigating the Sept. 16 incident in which Blackwater employees allegedly shot 17 Iraqi civilians had already granted a form of immunity to the Blackwater employees involved.

In the 1967 case of Garrity v. New Jersey, the U.S. Supreme Court held that the government can't extract a statement out of an employee -- say, a police officer involved in a shooting -- on the threat of losing his job, then turn around and use that statement against the employee in a criminal trial. In a subsequent decision, the court made it clear that Garrity's protection applies to independent contractors working for the government. State Department investigators looking into the Sept. 16 incident apparently offered Garrity deals to Blackwater guards: Tell us everything you know about what happened, but rest assured that your statements won't be used against you in court.

The grant of immunity itself does not preclude the prosecution of the guards -- assuming, for a moment, that prosecution is possible at all -- but it does make such a prosecution vastly more difficult. It's not just that prosecutors couldn't use the guards' statements; they would also have to persuade a court that they obtained whatever evidence they did use entirely independently from the guards' own statements. And if you don't think that's difficult, go ask Oliver North. Hint: You won't find him in prison.