Last March, the Buenos Aires legislature renamed a local subway station in honor of the Argentine journalist Rodolfo Walsh. Walsh is beloved in Argentina and hailed across Latin America as the pioneer of the so-called “nonfiction novel.” Not only did he found his own news agency, but he also published ten works including short-story collections, a pair of plays, and several books of narrative nonfiction; all of which earned the plaudits of such literary luminaries as Gabriel García Márquez. He was also famously a political activist, blending his two vocations into what he called “the violent profession of being a writer.” In 1977, hours after penning an open letter to the then-ruling military dictatorship, he was gunned down on the streets of Buenos Aires.

So why have you never heard of him? Cold War politics, coupled with Walsh’s embrace of a notorious leftist militant group called the Montoneros, surely have something to do with it. But the more immediate, and surprising, reason is that his best works have never before been translated into English. Daniella Gitlin’s skillful and fluid translation of Operation Massacre is welcome and long overdue.

Operation Massacre is Walsh’s account of the mystery surrounding a botched secret execution of alleged participants in a failed 1956 uprising by supporters of the recently deposed president Juan Domingo Perón. Six months after these events, Walsh, who was then twenty-nine, was sitting in a café when a man approached him and said cryptically: “One of the executed men is alive.” This phrase, paradoxical as it was, piqued Walsh’s interest. He went on to write a series of articles in a local newspaper about the killings; in 1957, he published a book-length account, titled Operation Massacre. After months of reporting, Walsh discovered that the police had rounded up a group of men, most of whom had nothing to do with the Peronist uprising; then had led them, without explanation, to a remote field to face a firing squad. The authorities’ ruthlessness was matched only by their incompetence: six of the twelve men survived.

Sixty-six years after the book’s publication, the strongest impression made by the work is the depth of its investigative reporting. Walsh tracked down each of the survivors, and in uncluttered, driving prose uncovers the truth of the killings and their subsequent cover-up. Walsh lays out his case against the authorities like a lawyer before a jury: “There is not one important piece of information in the text of Operation Massacre that hasn’t been matched and double-checked with the testimony of three or four people, sometimes more,” he writes in the appendix. Beyond his sleuthing, Walsh had an eye for literary detail. He used records of state radio broadcasts of Stravinsky (of all people) to establish the sequence of events on the night in question; that meant proving that the order from the Chief of Police of the Province of Buenos Aires to kill the men came before the public declaration of martial law, and thus in violation of due process. On the basis of this discovery, Walsh makes his most damning accusation against the State: “That is not execution. That is murder.”

Studies of Walsh’s writing frequently discuss the detective stories he wrote before Operation Massacre and his use of that genre’s structure, style, and conventions to weave his true crime tale. That’s all well taken, although there is also a decidedly cinematic influence in his prose. Throughout the book, situations and characters are frequently described by Walsh as film-like or “straight out of a movie.” The pacing of the narration and dialogue reads as much like a screenplay as it does a potboiler, and the central structure—the murder is announced on page one while the facts leading up to it are revealed slowly via literary flashback, with frequent foreshadowing, reaching its climax in a riveting dozen-page description of the shooting—is redolent of Sunset Boulevard or other film noir classics of that time period. (The book was eventually turned into a film in 1972 and became a sort of indie hit, shown widely and secretly despite limitations on political activity at the time.)

Gitlin nicely captures these elements and the fast-paced immediacy of his prose. The straightforward tone and swift pace, she writes in her translator’s note, can be deceptively complicated to translate, marked by frequent shifts in tense and register. The Uruguayan critic Ángel Rama once called Walsh’s writing “crime novels for poor people,” but, as Osvaldo Bayer writes in his introduction to the most recent Spanish-language edition, Walsh likely wouldn’t have taken this as a putdown: “[Walsh] was interested in being brief and clear so that the poor readers of crime novels would understand it.” Walsh’s compassion for his subjects is evident in some of the more lyrical passages of the book, like in his description of one of the victims, a working-class dockworker: “ He would have liked to be something in life, Vicente Rodríguez. He is teeming with great ideas, great gestures, great words. But life is fierce with people like him. Just having a life will be a constant uphill struggle. And losing it, a never-ending process . . . he never manages to transfer the sense of power that his vigorous muscles give him to the objective world around him . . . That’s when he understands that he is nobody, that the world belongs to doctors.”

In the afterword to the new English edition, Ricardo Piglia notes Walsh’s skill in capturing the dialogue of his mostly working-class subjects, writing that Walsh “knows how to hear the story that emerges from the popular voice and tries to get closer to the truth by using it.” This point underscores the main factor differentiating Walsh from Truman Capote (whose In Cold Blood was published nine years after Operation Massacre) and other practitioners of the “New Journalism.” To Walsh, formal innovation was not purely literary experimentation meant to engage an individual reader. Rather, it was a tool designed to capture and convince the widest public possible to demand justice. Unlike a classic crime novel, the villain in Walsh’s work is not a psychopathic individual, but a diseased, murderous State. Walsh is the epitome of the heroic “watchdog” journalist, who is tasked, as he declared in his famous last written words, “to bear witness during difficult times.” Nevertheless, the additional texts included in this volume show the gradual evolution of his expectations for the book. In the introduction and prologue to the first edition, he seemed hopeful about the book’s potential for broad impact; in later versions, he grew despondent and, eventually, indignant as justice remained elusive. By the time he wrote the final piece included in this edition—his fateful letter to the junta—an even more brutal dictatorship was in power, and he had joined forces with the Montoneros.

Walsh’s own murder at the hands of the junta became a symbol of the rampant impunity of the “Dirty War,” transforming him, in Bayer’s words, from “witness to protagonist” and he has continued to be a towering figure post-dictatorship. In the first decades of democracy, he inspired a new generation of investigative reporters to denounce injustice and corruption. In today’s Argentina, squabbles over his political and journalistic legacy have become an endless point of contention.

In 2011, a federal court sentenced 12 former military members to jail terms ranging from 18 years to life in prison for the murder of Walsh and 85 others (two men were absolved and other implicated junta members are no longer living). Though belated and imperfect, the writer’s story got the ending he had long sought for his protagonists. If the whole dramatic arc of Walsh’s life seems too improbable, like something ripped out of a novel, perhaps that’s because, as Bayer writes, “Rodolfo Walsh doesn’t exist. He is only a fictional character. The best character in Argentine literature. Only a detective in a crime novel for poor people. Who will never die.”