Whitey was an informant for the FBI for many years. He ratted out his competition. FBI arrested those guys, and looked the other way on the crimes Whitey did, including murder. One of the guys that killed Whitey was a mob guy doing life. Nothing to lose. Rumor has it they cut out his tongue. (Or tried to) Sounds like revenge to me.
Mueller was fbi director while burger was alleged fbi informant.