The Jack Nicholson film The Departed didn't tell half of their story. A poor kid from the slums, Robert Fitzpatrick grew up to become a stellar FBI agent and challenge the country's deadliest gangsters. Relentless in his desire to catch, prosecute, and convict Whitey Bulger, Fitzpatrick fought the nation's most determined cop-gangster battle since Melvin Purvis hunted, confronted, and killed John Dillinger. In his crusade to bring Bulger to justice,...