As noted before, in the Valerie Plame affair special prosecutor Patrick Fitzgerald knew in advance there was no crime and knew Scooter Libby wasn’t involved in the non-crime but brought him before a grand jury anyway.
George Jonas makes a good point. If misleading a grand jury is a crime then Fitzgerald himself should get a dose of justice:
It's grandstanding prosecutors who are politicizing justice,... I wouldn't jail Libby for 30 hours, but assuming he deserved 30 months for what he did, Fitzgerald should be looking at 30 years.
Update: Robert Novak sheds some more light on this in an interview with Hugh Hewitt:
HH: Let me ask you, I’m bored silly by the Plame affair, Robert Novak, but I do have one question about your opinion? Why was Armitage not charged if Valerie Plame’s identity was a secret, and Patrick Fitzgerald was investigating its leak?
RN: Because there was no crime committed under the Intelligence Agents Identity Act. That bill was passed, Hugh, to protect intelligence agents overseas from being outed by left wing forces, and then marked for assassination. It was really a readly serious act, nothing like somebody sitting in Langley in the CIA Headquarters as Mrs. Wilson was, doing analysis. There was no crime committed under that act, and therefore, he was not charged. And so that is the whole problem with the Libby indictment. He was charged for obstructing justice when there was no underlying crime committed, or allegedly committed.
HH: Why did Fitzgerald, do you think, in your opinion, continue on with the investigation once Armitage had revealed it was he who was the leaker?
RN: Because…you know, when he entered the case, he was told that Armitage was the leaker. That information was given to him, because it had been known for three weeks before he was named as special prosecutor. And therefore, I think the Justice Department should have bitten the bullet and taken care of him itself. Why he did not reveal that is something that is in the mysteries of the whole, strange relationship of special prosecutors. It is very difficult for them to say no crime was committed, you’ve named me for nothing, and I’ve established a staff for nothing. But that’s in fact what he should have done.
Which confirms that the prosecutor Fitzgerald was guilty of misleading everyone including the grand jury.