Actually, he hasn't been. It took a few months for Justice to get moving on this after the Novak article. I don't remember exactly what triggered the move, but I believe that it was Tenet making a complaint to either the White House or Justice.
Novak has stated publicy the leak did not come from the WH. What triggered it was Wilson going around talking about wanting Rove "frog marched" out of the WH in handcuffs. There's plenty to investigate, but rest assured, wrongdoing from the Bush WH will not be the finding.