But who appoints the special prosecutor? DOJ?
Interesting you asked. Because, you see, we've not had a special prosecutor at this level since Watergate. There have been several independent counsels since then (remember Kenneth Starr?), but the law authorizing the appointment of independent counsels expired in 1999. It was replaced by a separate division in the DOJ called the Office of Special Counsel.
Problem is that the guy who heads this office has, arguably, a conflict of interest. You see, he's from Illinois and is the lead prosecutor against Rod Blagojevich (case pending retrial after a hung jury on most charges in his first trial). It's hard to argue that Fitzgerald, the current office holder is truly independent.
So, you see, the waters are extraordinarily murky - legally and politically.