How Whitey Bulger Co-opted The FBI

All Things Considered interviews a former FBI agent who has written a book about Bulger:

Fitzpatrick was a young FBI agent with a solid track record when the bureau sent him to Boston to sniff out corruption in the office. One of his first tasks was to evaluate Bulger, who was supposedly providing information on Mafia activities in New England.
"I put out my hand to shake his hand, and he kind of turns on his heel and walks away," Fitzpatrick says. "He's evasive, he's not answering the questions, he's going all over the place, and so I make a mental reservation that I'm going to end this thing, I'm going to cut it short."
Fitzpatrick decided to "close" Bulger, to end his informant status with the FBI. But he found himself stymied at every turn by Bulger's handler, John Connolly, and higher-ups in the bureau.
Several witnesses approached Fitzpatrick with information tying Bulger to a murder. When two of them were killed, Fitzpatrick says he began to suspect there were leakers in the FBI's Boston office. But what he never suspected was that the leaks were coming from Bulger's handler, Connolly, and Connolly's immediate supervisor, John Morris.

The whole Bulger story is amazing.  I recommend reading Black Mass, also.  It is fascinating, with tons of Southie information.  The fact that Bulger's brother was the President of the Massachusetts Senate makes things even spicier.