Alderman Isaac "Ike" Carothers has been secretly recording conversations with public officials and real estate developers, the Chicago Sun-Times reported Friday.
The newspaper says it is unclear how many of Carothers colleagues may have been ensnared since the Sun-Times reported last year the alderman was under federal scrutiny.
Despite his cooperation, Carothers, whose father, former Alderman William Carothers, served time for corruption, was indicted Thursday on charges of accepting $40,000 in home improvements and other gifts from politically connected developer Calvin Boender, who has been charged with bribery.
The indictment accuses Carothers of taking gifts in exchange for promoting a zoning change that would benefit Boender.
U.S. Attorney Patrick Fitzgerald said the case should send a message to anyone who wants to bribe their way into City Hall access.
Fitzgerald made no mention of Carothers' cooperation