On August 4, 1944, Anne Frank, her family, and four others were arrested in Amsterdam by German Security Police (Grüne Polizei) following a tip-off from an informer who was never identified. From the article:
"Who Betrayed Anne Frank? Multiple people have been suspected of informing the Nazis of the Franks' hiding place, while one theory suggests it may have simply been bad luck. 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.
Investigators began taking a fresh look at the case in 2016, hoping to provide new answers. A 20-person team for the Anne Frank House was 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 hoped 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.
Meanwhile, in 2018, a new book claimed to offer evidence that Anne Frank and her family were betrayed by a Jewish woman who was executed after World War II for collaborating with the Nazis.
Multiple Suspects Named in Frank Family's Betrayal 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.
Was Anne Frank's Family Betrayed by a Fellow Jew? In a 2018 book, The Backyard of the Secret Annex, Gerard Kremer, the son of a member of the Dutch resistance of the same name, argues that a Jewish woman, Ans van Dijk, was responsible for the Franks' capture. Kremer's father was an acquaintance of Van Dijk in Amsterdam and Kremer writes that in early August 1944, his father overheard Van Dijk speaking about Prinsengracht, where the Franks were hiding, in Nazi offices. That same week, the Franks were arrested—while Van Dijk was away in the Hague.
The involvement of Van Dijk, who was executed in 1948 after admitting to collaborating in the capture of 145 people, had been previously claimed. But, the Anne Frank House museum and research center were unable to confirm Van Dijk's involvement after its own investigation.
Among other theories the Anne Frank House investigated was a 2016 report that suggests no one was, in fact, responsible for leaking to the Nazis. Instead, the group’s arrest could have been a tragic accident. That report, written by senior historian Gertjan Broek, 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, 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.'”