Whenever Timothy Ryback, who has written about the Holocaust for decades, starts a new project he asks himself, What would the world gain by another book on the subject—on Hitler, on the SS, on Dachau? It took him almost 20 years to answer this question for his newest book, Hitler’s First Victims: The Quest for Justice, about the first SS-perpetrated murders in the Dachau concentration camp in 1933, and the mission of a Munich prosecutor, Joseph Hartinger, to bring them to court.

Ryback first discovered Hartinger’s story in the early 1990s while in Dachau on assignment for The New Yorker. At face value, the story seemed a good one—Ryback marveled at the courage Hartinger showed in trying to prosecute the first commandant of Dachau—but one that had been told enough times. Ten years later, on a return visit to the Dachau memorial archives (Ryback was back this time for a New Yorker story on Pope Benedict XVI’s history with the Nazis), Ryback found the justification for a re-telling of Hartinger’s story. It was embedded in a 34-page confession that Hartinger had written in 1984 when he was 90 years old, after years of reticence on the subject. Reading the document, Ryback focused on Hartinger’s emphasis that the murder victims’ Jewish ethnicity was of deep importance to the case, which was something that, as Ryback understood it, nobody else was considering in the early stages of the Nazi regime.

That’s when Ryback realized that Hartinger’s story of prosecuting these first murders was at the precipice of the Holocaust. As Ryback explains over the phone from Paris, where he lives and works at the policy institute, Académie Diplomatique Internationale:

“I felt like this really brought together for the first time all of the constituent parts of what we know as the Holocaust, which is Nazi facility with barbed wire and watchtowers, and the intention to start selecting Jewish detainees from the others and executing them. And so I basically posit the notion that when we talk about the Holocaust and we say, When did it begin? I can say, a few minutes after five o’clock on Wednesday, April 12, 1933 and these are the first four victims of what we come to know as the Holocaust.”

And so Ryback undertook writing a version of Hartinger’s story that places the murders front and center as a historical mark. Details about the murder victims’ lives leading up to their incarceration in Dachau, which the author managed to find in obscure archives, are crucial to the success of his narrative, a kind of micro-history of the weeks surrounding the murders. Just as crucially, Ryback—unflinchingly, and in an intentionally understated fashion—details the torture and ultimate murder of several first Jewish detainees in Dachau, carried out by the SS.

“The devil was in the detail in these most horrific moments,” Ryback says in reference to one element of a Jewish detainee named Karl Lehrburger’s story that he found particularly chilling.

It was a moment in which Lehrburger saw some men he recognized from his hometown walking in his direction and slipped into the top bunk of his cell, trying to hide his face from recognition. When Lehrburger first arrived in Dachau, nobody from his town recognized him, so he could keep his Jewish ethnicity secret. But the men walking towards him that day were his town’s local gestapo. He was found out and executed. “What surprised me was how small this world was,” Ryback remarks. “When we think about how vast the Holocaust is, how mechanical and monstrous these processes were, yet at the very beginning it was so human, it was one human being, neighbors sometimes or people from the same town, recognizing each other.”

It is the element of human specificity that largely powers the most renowned Holocaust memoirs like Primo Levi’s or Elie Wiesel’s. Ryback wants to channel the reader’s attention to the concrete, human stories of these first-person Holocaust accounts. But he also maintains the historian’s larger-picture, analytical perspective. “It’s sort of this space in-between the two which is trying to make one understand the process through the experience of the human being and yet allowing one to see the dynamics that allow something to happen,” he explains. Hartinger’s story does mark an important moment in history but it is the way in which it intersected with the stories of the men imprisoned in Dachau that makes Ryback’s telling worth reading. It’s the attempt at answering, in a very concrete way, the how. “As I began writing the story, I realized that this really was the beginning of [the Holocaust],” Ryback says. “Person by person, phone call by phone call, letter by letter. That’s when I thought, This story is worth telling.”

Alexia Nader is a writer living in San Francisco and a senior editor of The Brooklyn Quarterly.