As Murray Waas pointed out for us at the Scotter Libby trial, Ari originally invoked the Fifth Amendment when called before the federal Grand Jury hearing evidence in the CIA leak case.

Fleischer ultimately testified under a grant of immunity.

Bush claimed publicly that everybody was cooperating fully and completely with the investigation, and that anyone who wasn't would be gone. In Ari's case, he left the WH before he took the Fifth, but the question remains: Was one of the reasons he left because he knew he was going to have to take the Fifth and in doing so ,place the Bush administration in an untenable political position?

And guess what else? Legal papers filed in the case seemingly indicate that at least one other previous or current administration official like Ari took a similar deal.

Expect Libby's lawyers to go after Ari hard during his cross examination. Fitzgerald indicated today that Ari was going to be a critical witness for the government.