For the last seven years, the German journalist Malte Herwig, a reporter at Suddeutsche Zeitung magazine, has arduously, conscientiously tackled the challenge of researching and writing a book about the postwar German government’s “double game,” as he calls it. In Die Flakhelfer (DeutscheVerlags-Anstalt), which comes out in Germany on Monday, he reveals that, for half a century, the German leadership sought to suppress the names of prominent citizens who were Nazi Party members in the Second World War while pretending to seek them, and while simultaneously pursuing the soul-searching process of coming to terms with Germany’s grievous Second World War history—a process Germans call Vergangenheitsbewältigung. Herwig finds this behavior troubling. In New York this week he explained the genesis of his book.

In 2006, Herwig was working as a reporter for Der Spiegel when he learned—along with the rest of the world—that Günter Grass, the Nobel-Prize winning author, had been a member of Hitler’s S.S. in the Third Reich. Herwig promptly called Grass for an interview. “I wanted to know from Grass, why did you keep stumm for so long, and why did you then out yourself?” he recalls. “Grass told me that, one morning, while he was in the bathroom shaving, he caught himself whistling the tune of an old Hitler Youth song, “Uns're Fahne Flattert uns Voran,” which is the tune of the Hitlerjugend. He said it made him realize how deeply the Third Reich had impressed itself on him, and he decided, as a writer, that his means of trying to come to terms with this would have to be his writing, so that’s what he did.” Shocked that such an admired postwar figure—an icon of conscience—could have concealed such a defining secret for so long, Herwig went to the Berlin branch of the Bundesarchiv, where files of the Nazi era are kept, to see if he would find other familiar names. What he saw in those files, he writes in Die Flakhelfer, was “a political-cultural pantheon of the German Postwar era.”

“They were the last people you would have expected to be members of the Nazi Party,” Herwig said. The names included “leftists, Communists after the war, very educated, upright democrats.” Growing up in the Federal Republic of Germany in the 1980s, Herwig had “learned about the Holocaust in high school, learned about the Third Reich, learned even about the crimes of the Wehrmacht [Germany’s army in the Second World War],” he said. “I really thought I lived in an enlightened age, and that Germany had come to terms with and owned up to its Nazi past. It was only when I discovered these files that I realized: Wow. There’s a lot of hidden information here that they didn’t tell us about.” He wanted to know, he said, why the names had remained hidden for so long.

In his book, Herwig reveals the answer he found to this question. For decades, “political leaders at the highest level of German government” deliberately delayed negotiations for the return of 10.7 million Nazi Party membership cards called Karteikarten, which clearly identified Germans who signed up for Nazi Party membership in the War era. Herwig calls the collection “a sort of central catalogue of shame.” After the War’s end, in 1945, the Karteikarten were safeguarded by American officials in Berlin, in a building called the Berlin Document Center (BDC), which had served as a Gestapo listening center during the Third Reich. Immediately after the War, the Americans used the cards in their denazification. “That lasted only lasted a year or two,” Herwig said. Afterwards, the American government held onto sensitive Nazi files for use in war crimes prosecution and for other purposes, but as early as 1952, U.S. official policy was that non-controversial documents could be “returned to the FRG at an early date.” “The Americans decided they had better things to do in the Cold War than upset their West German allies,” Herwig explained. But when, in 1968, the U.S. Mission Berlin suggested to the State Department that the BDC building and records be transferred to the German government, nothing happened.

“It was clear to anyone in Bonn that as soon as the files were back in German custody, it was a Pandora’s box that couldn’t be kept closed,” Herwig said. “So long as the Americans had it, it was safe.” Using the Freedom of Information Act in the U.S. and Germany’s similar law, the Bundesarchivgesetz, Herwig gained access to sensitive files in both countries. When, in the autumn of 2011, he first looked at American administrative documents about the Nazi files in the National Archives in Washington, he said, “I found the biggest postwar cover-up imaginable, it went all the way to the top of the state.”

For years, rumors had circulated that Daniel P. Simon, the American director of the BDC in Berlin in the 1970s and 80s, had a safe in which he kept the most compromising, potentially incendiary records—records that showed the past Nazi affiliation of contemporary German political figures. In Washington, Herwig learned that this sensitive file had in fact existed. He held its pages in his hands. “It’s the opposite of Schindler’s List,” he said. “I call it Simon’s List.” On ordinary sheets of paper, he saw typed lists of Nazi Party members, and penciled onto the margins, dozens of names that the Americans had added: German politicians of the 1970s and 1980s. “Every German cabinet, every federal government cabinet, from Adenauer to Kohl, contained former NP members right up to 1992,” Herwig said. Looking at those long-protected files, he realized, “I had hit the jackpot.”

He had also found vindication for his controversial subject of inquiry. Back in 2007, when Herwig began publishing articles in Der Spiegel about the public figures he unearthed in the Karteikarten, he provoked an angry backlash, which continued over time as he revealed the Nazi Party membership of more than a dozen prominent German politicians, intellectuals, and artists. “Whenever I wrote that I’d discovered a pillar of society who had a stain, people would say, ‘Oh god, he’s muckraking, he’s throwing dirt at these people, it cannot be true.’” He paused. “But sorry, it is: here’s the file.” He added, “It’s mostly liberal historians and journalists who protest; most of the people I expose do not. That is—” he clarified, “I don’t call it ‘expose,’ because I don’t do it in a judgmental way. I don’t want to smear anybody; I’m interested in the truth.”

The man who makes this statement does not look remotely vengeful. Herwig is tall, relaxed and bespectacled, and wears a tan linen suit. If anything, he resembles an amiable Englishman at a country house party (Herwig spent seven years at Oxford, where he got his doctorate in 2004, and also was a visiting research fellow at Harvard). But ever since he first looked at the Nazi membership cards in 2006 in Berlin, he has refused to be diverted from his project. “I realized I had to look at the Nazi past with fresh eyes,” he said. “There’s no point to wringing your hands in a ritual manner if you don’t try to understand what really happened. You must look into the gray areas of history, not only the black-and-white.”

He continued, “So far, all we’d been looking at was Hitler, Himmler and so on; or some sort of overwrought Goldhagen approach. But I thought, I’ve got to look at the people who are sacrosanct,” he said. “I am interested in broken biographies,” he added: “I’m interested in people who started out as youthful indoctrinated Nazis, and managed to turn themselves into democrats.” He had no desire to “cast blame on anyone who joined the Nazi Party as a child in wartime,” he emphasized. “What I can’t take is not owning up.”

Acquiring permission to consult confidential U.S. diplomatic memos from the Cold War era, Herwig found a paper trail recording American frustration at German stalling tactics. One of these memos, written in 1987 by the BDC’s Daniel Simon to the U.S. Mission Berlin, complained, “I am pretty well fed up with them [the German government] forever blaming us in public for foot-dragging with these transactions; when, in fact, if we were to offer them the BDC tomorrow without pre-conditions, no doubt in my mind exists that they would turn us down.” Another memo dates from February 21, 1990—a few months after the fall of the Berlin Wall—and sets out the Americans’ mind-bending assessment of the “German strategy.” To satisfy Bundestag members who were demanding the return of the Karteikarten, the Mission Berlin memo explained, “the German delegation will take a firm and uncompromising line regarding immediate transfer of the entire BDC or parts of it.” However, the memo continued, the German Foreign Ministry, headed by Hans-Dietrich Genscher (who was also Germany’s Vice Chancellor) “indicated no interest in exploring or developing any alternative compromise strategies,” and “fully expects to return to Bonn with a firm response from the U.S. against any immediate turnover.” Got that? Diplomacy is not for sissies.

In 1994, nearly five years after the fall of the Berlin Wall, the NSDAP files were finally handed over, the BDC closed, and the millions of Karteikarten moved to the Berlin branch of the Bundesarchiv. In 1992, perhaps in anticipation of that release (so Herwig believes), Genscher “abruptly” quit political life. “What was the first name that emerged from that bag of dark secrets at the Berlin Document Center in the summer of 1994?” Herwig asks rhetorically. “It was Hans-Dietrich Genscher. He applied to join the Nazi Party in 1944.” Once the news came out, Genscher said that he “had become a member of the Nazi party without his knowledge,” Herwig said. “That’s like Kissinger saying, ‘Chile? Pinochet? What?’”

Genscher, born in 1927, was part of the generation of German boys, born between 1926 and 1928, who were called upon to serve as child soldiers late in the war, manning anti-aircraft guns. They were known as die Flakhelfer—the flak helpers. Herwig makes clear in his book that he has no desire to assign blame, at this late date, to people who joined the Nazi party as adolescents, and who went on after the war to lead “blameless” lives, serving postwar Germany as “artists, scientists, politicians, journalists, lawyers.” “Given that they grew up in a dictatorship, they were ideologically conditioned by it, they were brainwashed. So I think it’s the most natural thing in a way; you would expect brainwashed little kids to join the Party, that doesn’t surprise me.”

What surprises and disturbs him, he said, is when his countrymen refuse to own up to their pasts; whether by claiming, like Genscher, that they did not remember signing up for the Party; or claiming, like one of the eminent Party members Herwig uncovered in 2009, the composer Hans Werner Henze, that they had not signed up at all: that they had somehow been incorporated into the Nazi Party without their knowledge or authorization. Herwig counters, “There were no collective secret inductions of people who didn’t know about it. You, yourself, did have to sign an application form to become a member of the Nazi party.” Many newspaper reporters deplored the release of such news, protesting, Herwig writes in his book, “that [Henze’s] lifelong artistic and political engagement was being reduced to atonement ‘by an unproven allegation.’”

Herwig profoundly disagreed with this attitude, he said. He considered it vital for the implicated people, as well as for their descendants and for modern-day German society, to admit these suppressed aspects of their shared history, and to reflect upon them. When, in 2007, he learned that Martin Walser, the acclaimed author of dozens of novels, had joined the Nazi Party in 1944, he called Walser for an interview. Walser, like Genscher, said he had been enrolled in the party without his knowledge. Herwig was skeptical. “Now, with hindsight, you read these works by Grass and Martin Walser, and you see that they circled the truth again and again in their work without going to the very core; to their membership in the Nazi Party. Their own membership was the blind spot, the historical heart of darkness that couldn’t be touched.” When you read them, he said, “You can sense it—their repressed membership—between the lines. It wants out.”

In 2012, Herwig interviewed the postwar German Chancellor Helmut Schmidt, who was 93, but still “very sharp in mind and tongue” and asked him, “Why do you think people like Genscher even today won’t admit to something as small as having applied to join the Nazi Party at 17, at the end of the war?” Schmidt answered in English. “He said to me: ‘Tell a lie and stick to it.’ I said ‘What do you mean?’ We continued in German, and he said, ‘Once you’ve decided to lie, after 1945, it’s very difficult later to tell the truth.’ Earlier that year, Herwig had discovered at the National Archives that the U.S. government had continued keeping track of the Nazi pasts of members of the German government “as late as 1980.” He asked Schmidt, he said, “‘Did you know the American government checked you out in 1980?’ and he said, ‘No, but I’m not surprised. There’s no foolishness I’d put past American intelligence.’ I said, ‘This wasn’t the CIA checking up on you; this was the State Department.’ He said nothing. He just had another cigarette.”

The story of the decades-long feigned tug of war over the Karteikarten is not only a German story, Herwig emphasizes, it’s a “German-American story,” he said. “The Americans analyzed the Nazi membership files as soon as they had them,” he said. “I don’t blame the Americans,” he added. “They were good partners and responsible guardians of those documents, in the context of the Cold War, in which this sort of information could be used against people to considerable effect,” he said. In his opinion: “The real culprits are the Germans.”

Back in the mid-1940s, when American officials in Berlin were engaged in denazifacation, they discovered that “one lie had very common currency among Germans who were asked about their affiliation with the Nazi regime,” Herwig said. “They would say they became members of the Nazi Party without their knowledge. This myth came about in 1946 or 1947, and still is told today. It is not true,” he said firmly. “I’m flabbergasted that this lie, this excuse, that came into currency in 1945, after the Americans arrived and swept across Europe, is still current.”

It was only three years ago, when he was 37, that Malte Herwig found out that his own grandfathers had both been Nazi Party members. How did he unearth this long-buried secret? “It was very simple,” he said. “I just asked. My family had never volunteered the information, but as soon as I asked, they didn’t hesitate to answer. That is the main reason I wrote this book,” he said. “I wanted people to start asking the right questions, not only in my family, but in the Bundesrepublik as a whole.”