On August 4 1944, SS officer Julius Dettman received information that Jews were hiding in a warehouse complex at Prinsengracht 263 in central Amsterdam. The IV B4 “Jew-hunting unit” that he dispatched to search the warehouse found eight Jews in its annex, including four from one family: German-born Otto Frank, his wife Edith, and their two teenage daughters Margot (18) and Anne (15). 

Incredibly they had been hiding in the annex for 25 months, during which time Anne had kept a journal that was published after the war as The Diary of a Young Girl. Tragically Anne perished in a Nazi death camp, as did her mother, sister and the other four residents of the annex. Only Otto Frank survived.

The question that has tormented historians ever since is: who betrayed the Franks? A number of possible culprits have been identified in books: Lena Hartog, the wife of the assistant warehouse manager, a shady character called Anton ‘Tonny’ Ahlers, and the Nazi-sympathising sister of Bep Voskuijl, a company employee who was helping to hide the Franks. But the evidence in each instance is far from convincing.

In 2016, a fresh attempt to crack the case was launched by Dutch filmmaker Thijs Bayens and journalist Pieter van Twisk. Using funds from a variety of sources, they recruited a 23-person Cold Case Team led by former FBI special agent Vince Pankoke that included a behavioural scientist, historians and, from the spring of 2019, Rosemary Sullivan, a prize-winning Canadian biographer and the author of a new book about the investigation, The Betrayal of Anne Frank.  

Based in an office in northern Amsterdam, the team gathered documents from 29 archives and used modern law enforcement techniques such as criminal profiling and forensic testing to narrow the search.