When a federal Bill of Information is used as the means to deliver charges against an individual, rather than via a Grand Jury indictment, it is almost always a sign that a defendant has agreed to testify against someone in exchange for leniency.
Legal analysts tell WWL Radio that "unnamed public official" at the center of the investigation is Nagin.
Williams served as president of Three Fold Consultants LLC. The filing says the unnamed official took payoffs in exchange for using his office to steer city work to Williams between 2007 and 2010.
It also accuses Williams and "Public Official 'A'" of creating and using corporate documents "to disguise the true nature of the payoffs."
A different businessman, Frank Fradella, pleaded guilty in June to making a $50,000 payoff to an unidentified former city official whose tenure also matched Nagin's.
Nagin has not been charged with a crime. His attorney, Robert Jenkins, said he hadn't heard about the case against Williams and declined to comment.
In February, people with direct knowledge said federal authorities were investigating questions about free trips and gratuities that Nagin allegedly accepted while in office. They spoke to The Associated Press on condition of anonymity because they could not publicly comment on an ongoing investigation.
Williams, who was charged Nov. 16 in a sealed bill of information, is scheduled to make his initial court appearance on Monday. Court records show he is scheduled to plead guilty Wednesday before U.S. District Judge Susie Morgan.
Brian Capitelli, one of Williams' lawyers, declined to comment.
In the case against Fradella, prosecutors say he provided truckloads of free granite to the unidentified official. Nagin and his two sons obtained a contract to install granite countertops for local Home Depot stores after Hurricane Katrina struck in 2005.
A lawyer for Nagin's two sons, Jeremy and Jarin, told a local newspaper and television stations in October that his clients were summoned to appear before the grand jury investigating their father.
Fradella, who is scheduled to be sentenced in March, was CEO of Home Solutions of America Inc., a publicly traded disaster reconstruction firm.