On August 4, 1944, police in Nazi-occupied Amsterdam raided a warehouse and arrested eight Jews who were hiding in an annex disguised behind a bookcase. Among those captured was Anne Frank, a 15-year-old schoolgirl who had spent over two years living in the cramped safehouse with her parents and older sister. The diary Frank kept during her confinement is now considered one of the most important accounts of the Holocaust, but the circumstances of her arrest have always been cloaked in mystery. It is believed that an anonymous tip helped guide the Nazis to the secret annex, yet despite decades of investigations, the identity of the informant has never been proven.

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Copies of Anne Frank’s diaries are on display at the Anne Frank museum in Amsterdam, Netherlands. (Credit: ADE JOHNSON/epa/Corbis)

Now, however, investigators are taking a fresh look at the case, hoping to provide new answers before the 75th anniversary of the famous arrest, in August 2019. The 20-person team is led, in part, by two retired FBI officials; former special agent Vince Pankoke, and behavioral scientist Roger Depue. As The New York Times reported, they hope to bring new technology, including forensic accounting, computer modeling and even crowd sourcing research, to examine existing evidence such as Anne Frank’s diary and the Amsterdam building where the Franks hid.

Anne Frank’s father Otto—the only member of the family to survive their subsequent deportation to the concentration camps—was among the first to assert that a betrayal had led to their capture. The group’s hideout was located inside a warehouse he had once owned, and they were aided by several of his employees as well as other Dutch sympathizers. Shortly after World War II ended, Otto Frank suggested that the culprit was Willem van Maaren, a warehouse employee who was not in on the secret. Van Maaren was later the subject of multiple investigations related to the betrayal—including one by famed Nazi hunter Simon Wiesenthal—but he always maintained his innocence, and none of the cases ever produced any evidence against him.

In the years since Anne Frank’s diary was published, investigators and historians have proposed several other potential informants. These include Lena Hartog, the wife of one of the warehouse employees; and Nelly Voskuijl, the sister of one of the Franks’ helpers. In 2002, meanwhile, author Carol Ann Lee argued the informant was Tonny Ahlers, a Dutch Nazi sympathizer who had previously been a business associate of Otto Frank. Ahlers’ own son endorsed the theory that his father was the culprit, but a subsequent investigation by Dutch authorities found no hard evidence of his involvement.

A key component of the new investigation will be a focus on previously unexplored material (including millions of documents in U.S. and European archives) and new theories. As Pankoke said, “We need to verify stories as they come in, and we know that is going to lead to further investigation.” The team is currently raising funds to support the investigation, which will showcased online and in a planned documentary produced by filmmaker Thijs Bayens.

Anne Frank in 1940.
Anne Frank in 1940. (Credit: Collectie Anne Frank Stichting Amsterdam)

Among those recent theories was a report that surfaced in 2016, in which Amsterdam’s Anne Frank House suggested that the group’s arrest could have been a tragic accident. That report, written by senior historian Gertjan Broek (who will also serve as an advisor for the new investigation), argued that the German Security Service might have simply stumbled upon the eight Jews while raiding the premises to search for fraudulent food-ration cards. Nevertheless, its researchers do not rule out the potential that Frank and the others were the victims of a betrayal. “Clearly,” the museum’s report concludes, “the last word about that fateful summer day in 1944 has not yet been said.”