A federal criminal complaint against Chicago Ald. Ed Burke filed Thursday accuses the 14th Ward alderman and chair of the City Council’s powerful Finance Committee of using “his position as an Alderman – including his apparent ability to withhold his official support for the building permit and a related driveway permit – in order to corruptly solicit unlawful personal financial advantage in the form of fees arising from the retention” of his property tax law firm, Klafter & Burke.

This is isn’t the first time a Chicago lawmaker has been charged with a federal crime, but this case bring up several questions: Do federal prosecutors have a strong case against Burke? Why did they file a criminal complaint instead of an indictment? And what does it mean that the U.S. attorney’s office says the investigation is ongoing?

Former federal prosecutor Renato Mariotti says extortion cases such as these can be difficult to prove because there’s often not a specific quid pro quo, but he said the “wiretap does a lot of the work … in getting prosecutors across the finish line.”

However, he said it can be more difficult to prove attempted extortion, as opposed to a completed extortion scheme.

Mariotti, who is now a lawyer with Chicago’s Thompson Coburn LLP, said it “looks like a pretty strong case to me, at first glance” and will likely be “pretty convincing to a jury.”

Mariotti said he expects that more information is apt to be revealed in an expected forthcoming indictment.

Related stories:

Ald. Ed Burke Charged with Attempted Extortion

Ald. Ed Burke Holds High-Dollar Fundraiser Amid Federal Probe

Embattled Ald. Ed Burke Facing Re-Election Challenge

What FBI Raid Could Mean for Chicago’s Most Powerful Alderman

FBI Raids Offices of 14th Ward Ald. Ed Burke