Tompkins said in February, Cannon closed a $25 million deal with an undercover agent and received $20,000 in cash.
She said they're determining if other people were involved in this kind of behavior, or if it was limited to Cannon.
The investigation has been going on for nearly four years, according to FBI Special Agent in Charge John Strong.
Strong said agents are still following leads in this investigation, which could result in more charges, and more people being implicated.
The U.S. Attorney's office said in a press release today, "Former Mayor Cannon used his elected official position to enrich himself at the expense of the City of Charlotte. Through his actions, Cannon betrayed the trust of his constituents and his peers, compromised the integrity of our local government and damaged Charlotte's good reputation as a city that does business the honest way."