It is not illegal for Cheney, Bush or a number of all to KNOW the status or existence of Plame/Wilson. It is even not illegal for Cheney to question certain staffers as to if Wilson's role had anything to do with the findings of Wilson's (Joe) trip to Niger.

However, it is illegal to disclose her status. Libby lied at least three times how he found out about her. He stated he heard it from at least three different reporters before he told another reporter. Now, the question is, and I think we all know who it now is (Official A - Rove), how did Libby actually find out about Wilson? But for a criminal prosecution Fitzgerald doesn't "know" that because Libby continued to lie about it. Further, if both Rove and Libby neither fess up to Rove telling him about Wilson and there is no third witness, Fitzgerald would have a hard time proving that Rove outed Wilson. It's that simple.

All of the answers to your questions are there in Fitzgerald's press conference. He said he would not charge an offense or talk about it if it could not be proved. With the lying going on, at this time, he can't prove the original offense.