Among the things President Barack Obama and others involved in picking a successor will have to consider is whether to select another outsider like the New York-born Fitzgerald or one of Chicago's prominent attorneys.
Might a woman lead the office for the first time in the nearly 200-year history of the Northern Illinois judicial district? And could his replacement drastically change the way the dogged, uncompromising Fitzgerald ran the office for 11 years, pursuing powerful politicians, moguls and mobsters?
"Chicago is in such a pivotal position — every sort of legal case comes up here," said Phil Turner, a former prosecutor at the Chicago office. "So, as U.S. attorney you affect not just Chicago or Illinois — but the whole nation."
At his Thursday news conference, Fitzgerald, 51, carefully sidestepped questions about specific names, saying only that it's important "the U.S. attorney be somebody that's independent."
Fitzgerald said he spoke this week with Illinois' top-ranking U.S. senator, Dick Durbin, about issues surrounding possible replacements — but hastened to add a malfunctioning smartphone complicated that discussion.
"He may have had a conversation with me" about successors, Fitzgerald laughed. "But I had no idea what he said."
Obama will nominate the replacement, but U.S. senators from Illinois have some say. The Senate must confirm the nominee.
Anton Valukas, who held same U.S. attorney's job in the 1980s, said he'd be surprised if Democrats try to permanently replace Fitzgerald before the presidential election and that he expected an interim U.S. attorney to be named while "a serious search" begins.
While Turner says many female candidates would qualify, he wonders if Obama might be reluctant to name one now, potentially opening himself up to attacks of using such appointment to win re-election votes from women.
And there's the question of where the replacement comes from. Former Illinois Sen. Peter Fitzgerald, who recruited Patrick Fitzgerald for the job in 2001, has said he believed the New Yorker's outsider status gave him freer rein to crack down on Illinois' corruption.
But many legal observers say there's no reason that many candidates with strong independent streaks can't be found in Chicago or elsewhere in Illinois.
Former federal prosecutor Joel Bertocchi said one could even argue that an attorney with depth of experience in Illinois and inside the U.S. Attorney's office in particular should have a leg up on a comparable outsider.
"I would say you need to know how that particular office runs," he said.
Fitzgerald, a Brooklyn, N.Y., native, advanced his career one criminal case at a time and earned a reputation as a hard-working anti-corruption prosecutor.
As an assistant U.S. attorney in New York, he successfully prosecuted major terrorism cases, including against those accused in the 1998 bombing of two U.S. embassies in East Africa and in the 1993 World Trade Center bombing.
Despite Fitzgerald's own successes — including prosecuting two former Illinois governors — Turner says an intimate understanding of just how Illinois corruption has worked over years should be high on the list of qualifications.
"Doing the job requires having a well-developed sixth sense of how things work around here," he said. Fitzgerald, he argued, didn't always have that.
Turner, who now works as a defense attorney, says private lawyers are hoping for some differences in approach. Fitzgerald had a reputation as too uncompromising, Turner said, someone fond of throwing the book at defendants.
"You jaywalk and he's charging you with conspiracy," he said.
Legal observers also caution there's a tendency to give too much credit to the top prosecutor when a massive support staff, the FBI and other agencies did the bulk of the work.
On Thursday, Fitzgerald said as much himself.
"I've actually been in the shower and heard someone on the radio say the U.S. Attorney did something today," he said. "And I had no idea I had done that, because other people had done it."
Fitzgerald's announcement that he was resigning comes not long after former Gov. Rod Blagojevich reported to a Colorado prison to serve his 14-year sentence. On the day of Blagojevich's 2008 arrest, Fitzgerald drew scrutiny by characterizing the former governor's actions as a "political corruption crime spree" that would "make Lincoln roll over in his grave."
A regretful-sounding Fitzgerald chalked that impassioned comment up to too little sleep and too much coffee.
"It sounded like a good idea at the time," he said Thursday.
Fitzgerald said he hadn't made any decision about what he'll do next, though he ruled out elected office. He did say, however, he could see himself accepting another government position.
"Whenever the phone rings in the future and the (caller) ID says 'public service calling,' I (will) answer the phone," he said.
Associated Press writers Tammy Webber, Don Babwin and Jason Keyser in Chicago.
Copyright 2012 The Associated Press.
(AP Photo/Kiichiro Sato)