Daniel Lee spent the best part of the last decade chasing the story of Robert Griesinger across Europe.

Griesinger’s name doesn’t appear in any histories of the Third Reich. Instead, the University of London academic suggests, he was simply an “ordinary Nazi” – an ambitious young lawyer who rose through the ranks of Württemberg’s civil service, worked for the Gestapo in Stuttgart, and eventually helped supervise the flow of Czech slave labour from occupied Prague to feed Hitler’s war machine.

But, as Lee argues in his new book, The SS Officer’s Armchair, Griesinger’s life throws a novel light on how Nazi rule was possible. “The famous fanatics and murderers could not have existed,” he writes, “without the countless enablers who kept the government running, filed the paperwork and lived side-by-side with potential victims of the regime.”

“I wanted him to represent or stand in for some of these millions of people who have just totally vanished from the historical record and whose story probably won’t ever be told now,” Lee explains in an interview.

The book is no dry academic treatise, but a page-turning piece of detective work in which the Jewish historian painstakingly weaves together scraps of evidence to assemble a fascinating portrait of an ordinary man who helped perpetrate extraordinary crimes.

Lee, a lecturer in modern French history, happened upon Griesinger by pure chance. At a party in Florence, the historian was asked by a fellow guest whether he could help her mother with an unsettling discovery. Jana, a Czech émigré living in Amsterdam, had taken an armchair she had purchased in Prague in the late 1960s to be reupholstered. The appalled chair restorer found in a cushion a bundle of swastika-covered documents.

Jana knew nothing of the documents’ origins or how they came to be in her cherished armchair. However, they set Lee off on a trail that took him from Prague to Berlin, Stuttgart, Zurich, a swathe of provincial German towns and even New Orleans.

Initially, he had little to go on. The documents – wartime passports, war bonds, uncashed stocks and share receipts, and a civil service exam certificate – revealed that their owner was a lawyer born in Stuttgart in 1906 who had been sent to work in Prague in 1943. But they gave away precious little else about Griesinger.

In archives in Prague, Lee secured his first major breakthrough: the discovery that Griesinger had been a member of the SS. His SS file in Berlin revealed that Griesinger had a family. And in Stuttgart, the historian’s patient cold-calling of all the Griesingers listed in the phone book led first to the SS officer’s nephew, Jochen, and thence to his two daughters, Jutta and Barbara.

More revelations were slowly unearthed as Lee trawled further archives and was granted access to long-stowed away family papers.

The picture which emerges is an unsettling one. Griesinger’s comfortable, idyllic childhood was a world away from the broken, impoverished family backgrounds which characterise the lives of many Nazi perpetrators. Indeed, believes Lee, even as he left university and began work as the Great Depression struck, it was not inevitable that Griesinger would become a Nazi.

However, Griesinger’s upbringing in an upper middle-class, nationalist and military family — set against the backdrop of Germany’s traumatic and humiliating defeat in 1918 — later made him, Lee argues, “more susceptible than most” to the siren call of Nazism. His mother’s diary, for instance, reveals a woman who both idolised her son and was deeply anti-communist, antisemitic and virulently right-wing. Further ingredients were added to this noxious mix in 19th century New Orleans, where Griesinger’s father was born at a time of heightened racial tensions in the years after the Civil War. Griesinger, Lee writes, inherited from his father and beloved grandmother “an ease with brutally racist attitudes and practices”.

Although Griesinger was not a Nazi party member in 1933 — “he might have found them a bit vulgar,” suspects Lee — within a few months of Hitler coming to power “he knew which way the wind was blowing” and signed up as a member of the SS. But the historian suspects that Griesinger was not simply an opportunist. “There were certain elements of Nazism that he was extremely attached to ideologically,” he believes. “He almost certainly did not vote for the Nazis [but] he nevertheless was able to enter the regime and to wear it like a glove.”

One of Lee’s most starling discoveries was that, while he was serving in Württemberg’s Ministry of the Interior and helping to implement the Nazis’ raft of antisemitic legislation, Griesinger’s neighbours were Jewish. Lee visited the house in Stuttgart and saw “how enmeshed these two lives were”. Griesinger would have daily walked past the mezuzah by Fritz and Helene Rothschild’s front door; from the garden he could easily have seen them lighting Shabbat candles in their kitchen.

During the war, Griesinger took part in the invasion of the Soviet Union. As he tracked his unit’s progress through Ukraine, Lee realised that Griesinger had passed through the shtetl which his great-grandfather had left as a boy but where other members of his family later perished.

Lee doesn’t know whether Griesinger participated in the atrocities which the marked the Wehrmacht’s progress through the blood lands of Eastern Europe, but he has no doubt that he knew just what was going on. Similarly, Griesinger was aware of the fate of those rounded up and tortured in the Gestapo’s cells as he sat in his suit and tie in an office close by. His later work for the Ministry of Economics and Labour in Prague saw him play a part in transporting tens of thousands of Czechs to work as forced labourers in Germany, as well as “controlling the destiny” of the small number of Jews who continued to slave away in the Protectorate of Bohemia and Moravia until they were transferred to the likes of Theresienstadt. “People like Griesinger,” argues Lee, “were entirely responsible.”

Thanks to the recollections of Griesinger’s eldest daughter, Jutta, the historian is also able to paint a vivid picture of the family’s charmed life in Prague: the maid, chauffeur and gardener who attended to their every need; the lavish dinner parties; and the sound of Verdi playing on the record player as her father relaxed of an evening.

“I could not have written this book without them,” Lee says of Griesinger’s now elderly daughters. “It was extraordinary how they were willing to open up to me and just talk.” That willingness, he realises, rested partly on the womens’ desire to hear what Lee’s research had turned up about their father. Some of it was clearly shocking and painful: believing him simply a lawyer, neither knew that Griesinger had been a member of the SS, for instance.

Lee admits that he’s been unable to solve one mystery: how Griesinger came to die in Prague in autumn 1945. Did he, as the official records suggest, die from an infectious disease in hospital — or was he, as his nephew suggested, murdered; one of countless Germans killed by Czech partisans and the Red Army in the aftermath of the liberation of the country after six years of brutal Nazi occupation?

That mystery may never be solved. But Griesinger’s death is perhaps the least interesting aspect of Lee’s utterly compelling life of this “ordinary Nazi”.