Does the world really need another book about the infamous Boston gangster James “Whitey” Bulger? That was the question foremost on my mind three years ago when I sat down to write Where the Bodies Were Buried: Whitey Bulger and the World That Made Him.

At last count, there have been 16 books about Bulger, with another half dozen or so on peripheral issues related to the Bulger story. There was also a feature documentary, Whitey by director Joe Berlinger, that was shown in theaters and on CNN. And now there is a major motion picture, Black Mass, starring Johnny Depp as Bulger.

The prospect of adding to this media assembly line was daunting. How does a writer come up with a new angle on a subject in the face of an oversaturated market? Given that the public might already perceive they know everything there is to know about Bulger, was it even worth the effort?

The conclusion I came to was yes. Not only was another Bulger book possible, it was necessary. In the rush to capitalize on a hot media story, quantity does not always equal quality. In the case of Bulger, many of the books were parochial, focusing on narrow aspects of the story. Some were written by criminal associates and rivals. A few were written by former law enforcement people who investigated Bulger’s criminal operations. Others were written by family members of victims who were killed by Bulger and his gang. The best of the bunch, including Black Mass, the book on which the Johnny Depp movie is based, were firmly rooted in what I call the cult of Bulger: it had an overwhelming fascination with the personal characteristics of the mobster that mitigated a broader analysis of how he achieved his power.

The question remained: how did Bulger rise to such a privileged position in the Boston underworld in the first place? Bulger was not your average gangster. Along with killing people (he was charged with 19 counts of murder) and engaging in a smorgasbord of racketeering activities—illegal gambling, narcotics, extortion, etc.—he was secretly a top echelon informant for the FBI. By forming an alliance with the feds, he was protected from prosecution. He remained a power in Boston’s criminal underworld for 20 years, from 1975 to 1995. When he was tipped off by his former handler in the FBI that he was about to be arrested, he disappeared and remained at large for 16 years until his capture in June 2011.

Everything from Bulger’s criminal exploits to his love life had been detailed in other books, but what was lacking was historical context. This was the canvas on which a broad social history was possible, and even essential, to understanding what was, arguably, the worst U.S. criminal justice scandal of the last half-century.

Long before Bulger came along, FBI agents in New England were using informants to stir up homicidal rivalries within the Boston underworld. Specifically, in the mid-1960s the FBI used a notorious contract killer for the Mafia, Joseph “Animal” Barboza, to testify in court and finger four men for a murder they did not commit. This travesty of justice, which was covertly authorized all the way up the chain of command by director J. Edgar Hoover, became the dirty little secret of the criminal justice system in New England. Much effort was made by many within the system to cover up this injustice, in the interest of preserving Barboza’s credibility as a witness against the Mafia.

Two key handlers of Barboza were instrumental in recruiting Bulger and his criminal partner, Stephen J. Flemmi, as FBI informants. One aspect of this alliance was that all involved—including men on both sides of the law—became custodians of the system’s dirty secrets, which included framing innocent people.

The historical continuity of corruption from the Barboza era to the Bulger era is the Rosetta stone for understanding how such a pernicious injustice was allowed to remain hidden and eventually metastasize into the phenomenon of Bulger.

No two-hour-plus movie could encapsulate the full scope of the Bulger story; a 438-page book is barely able to do it justice. Previous books have given short shrift to the long history of institutional corruption that helped create Bulger, making it difficult to see the forest through the trees.

Occasionally, a saturated marketplace creates its own demand. In this case, what was needed was a book that incorporated all that came before, but also went beyond the cult of Bulger to detail, once and for all, the universe of corruption that gave rise to and then enabled his reign.

T.J. English is the author of New York Times–bestseller The Westies, and most recently Where the Bodies Were Buried (Morrow).