It should have only taken Fitzgerald 15 minutes to determine that a crime was committed that Plame was an active covert agent and then "outed". And as soon as he found the truth- Plame's job at the CIA being classified as unclassified, the investigation should have ceased.
But surely as the the sun rises in the east and sets in the west, Fitzgerald abused his prosecutorial position by continuing this farce to see how many Bush administration he could entrap.
If my memory is any better than Libby's, then I believe part of Fitzgerald's directive by the President was to find the source of the leak. It was not just to determine whether a prosecutable crime was committed by any Bush administration official.