In Gilbers’s Germania (St. Martin’s, Dec.), the SS force a Jewish former police detective to catch a serial killer.

Where did you get the idea for this book?

I had long thought of writing a story set in the final phase of WWII. As an avid reader of crime novels, it seemed a no-brainer that I should work within that genre. I love cinema, so the movies Fritz Lang directed before emigrating were my starting point. In M and The Testament of Dr. Mabuse, the character of Commissioner Lohmann appears. I asked myself how Lohmann’s life would have played out during Nazism if he was Jewish. That was the inspiration for my main character, Oppenheimer. Storywise, this unthinkable situation opened up many interesting angles.

Was there also a real-life inspiration for Oppenheimer?

I was partly inspired by Ignatz Bubis, the former chairman of the Central Council of Jews in Germany. He would become furious when people insinuated that Israel was supposed to be his real home country. He saw himself as German—and of course he was. So I created Oppenheimer as a kind of German everyman, who just happens to be Jewish, like other people are Protestant or Catholic.

Did anything in your research surprise you?

I knew from the diaries of Victor Klemperer that during the war a small number of survivors still lived in the so-called Jew houses in the larger cities such as Berlin. Of course, the housing conditions were awful, and the residents were discriminated against in many ways. But I would never have thought that those Jew houses still existed until the beginning of 1945, when the last wave of arrests happened.

What was the hardest part of writing it?

Research was quite difficult, because it took me one and a half years to get thoroughly acquainted with my subject. I had no direct testimonies available, so in order to really immerse myself in that historical period, I used many contemporary sources like diaries, newspapers, and photographs—while constantly fact-checking, of course. During research I didn’t write a single sentence of my novel, and never imagined that the preparation would take so long. It was a big gamble on my part, because I wrote the novel on spec. By the time I finished it, I had spent two and a half years studying exclusively Nazism and serial killers. And that was not a particularly pleasant time for me, dealing with my country’s original sin.