After his arrest and imprisonment in 1999, he became a cooperating witness. His testimony is viewed as responsible for the convictions of FBI agent John Connolly and mobster Stephen Flemmi. Since his release from prison, he has written the bestselling true crime memoir, Brutal: My Life in Whitey Bulger's Irish Mob and Where's Whitey?, which was also written with Phyllis Karas, a fictional novel using Bulger as a character. Promotion for the book started on the day the FBI stepped up its efforts to catch Bulger with an advertisement; Bulger was caught two days later.