"The New York Times explained the relationship this way: “In the 1980's, while [FBI Agent]
Mr. Connolly was working with Whitey Bulger, Mr. Mueller was assistant United States
attorney in Boston in charge of the criminal division and for a period was the acting
United States attorney here, presiding over Mr. Connolly and Mr. Bulger as a ’top-
echelon informant.' Officials of the Massachusetts state police and the Boston Police
Department had long wondered why their investigations of Mr. Bulger were always
compromised before they could gather evidence against him, and they suspected that
the FBI was protecting him.”
[https://www.nytimes.com/2002/05/24/us/trial-ending-for-boston-fbi-agent-accused-of-mob-ties.htm]