Kwame Kilpatrick and the others associated in the case are facing charges under the federal RICO statute (Racketeer Influenced and Corrupt Organizations). You can check the FBI's glossary of terms to see what activities can be charged under RICO. The law was enacted by Congress 40 years ago to prosecute the leaders of organized crime. Before RICO it was difficult to prosecute organized crime leaders who rarely got involved in day-to-day dirty deeds.
Jim Schaefer of the Detroit Free Press has written up a nice little summary of RICO and how prosecutors have since used it to fight corruption in organized labor, drug gangs, and government officials. He writes:
Prosecutors must prove that there was a “criminal enterprise” at work; that the person being prosecuted conspired with others to commit a pattern of crimes, from violent acts to financial crimes such as bribery, money laundering, wire fraud or extortion.
Federal prosecutors will try to prove that Kilpatrick and those newly indicted today colluded in a pattern of crimes.