Steve "The Rifleman" Flemmi and John Connolly were both convicted following an investigation into corruption and other criminal activity within which U.S. government agency?
John Connolly (FBI): John Joseph Connolly Jr. (born August 1, 1940) is a former FBI agent who was convicted of racketeering, obstruction of justice and murder charges stemming from his relationship with James "Whitey" Bulger, Steve Flemmi, and the Winter Hill Gang. Stephen Flemmi:  Beginning in 1975, Flemmi was a top echelon informant for the Federal Bureau of Investigation (FBI).
FBI