Over 30 people have been accused of betraying the Franks and their friends. In 1947 and in 1963, investigations were opened to find if an overly-curious warehouse employee who worked beneath the hiding place betrayed the group. Wilhelm Geradus van Maaren said that he wasn't the informant and due to a lack of evidence, he remained uncharged.
Lena Hartog-van Bladeren, another suspect who helped manage pests in the warehouse was said to have suspected that people were hiding in the warehouse and started a rumor, but it was never confirmed that she knew that anyone was hidden there until the raid.
The rest of the suspects also remained uncharged due to a lack of evidence to prove or disprove any involvement.
The Cold Case Diary team, a group of over 20 forensic, criminology and data researchers are working to narrow down the suspect list. Led by retired FBI agent Vincent Pankoke, the team is working the case like a modern cold case. They've been searching through archives and interviewing sources while using more up-to-date technology to crosscheck leads. They've even created a 3-D scan of the hiding place to see how sounds may have traveled to nearby buildings.
The forensic team is also using artificial intelligence to find connections between people, places and events connected to the case.
A data science company, Xomnia, made a custom program that, among other functions, analyzes archival text to create nuanced and layered network maps.
"What you can do is try to see how often, for example, words or names are used together. If certain names are used together a lot, you can create kind of a network and do some kind of network analysis," says a lead data scientist at Xomnia Robbert van Hintum. One possibility is to cross-reference addresses with family relations and police reports to see who might have been involved or aware of various occurrences in the neighborhood.
"By adding all these dimensions together, an image emerges which you weren't able to see before," explained the Xomnia researcher.
The Cold Case Diary team will announce the findings in a book expected to be published next year.
The lead researcher with the Anne Frank House in Amsterdam, Gertjan Broek, actually believes that the focus on looking for an informant may actually be keeping researchers from finding the real reason that the hidden rooms were found.
"By asking ‘Who betrayed Anne Frank?’ you actually assume tunnel vision already. You leave out other options," said Broek.
The researcher holds that there's a possibility that there was no informant. The Franks and their friends may have been found by accident, during a search concerning fraudulent ration coupons.
The few facts that have been verified from the day support this theory. For one, the German and Dutch officials who arrived at the scene did not have transportation ready for the hidden people and had to improvise on the spot. Also, one of the three officers known to be at the raid was part of the unit the investigated economic crimes. Two men who provided the hidden people with black-market ration coupons were arrested, although one of their cases was dismissed for unknown reasons. It could be that a deal was made by one of the men.
Although it's a plausible theory, Broek cannot prove it, according to National Geographic. "No conclusive evidence in the end, of course, unfortunately," said the researcher. "But the more flags you can pin on the map, the more you narrow the margins of what's possible and that’s the main virtue."
Although it may be too late to bring the informant to justice, the research may still serve a purpose. "By better understanding what happened there, we can learn how people treat each other and prepare for the future," said Emile Schrijver, the general director of the Jewish Historical Museum and the Jewish Cultural Quarter in Amsterdam.
Anne Frank and her family hid in the secret annex on Prinsengracht in Amsterdam, where she wrote the bulk of her famous diary. Frank and her family, along with four other people and the family's helpers, Johannes Kleiman and Victor Kugler were arrested on August 4, 1944.
Anne Frank and her family were deported to Auschwitz on September 3, 1944.
Frank eventually died from typhus in the Bergen-Belsen concentration camp the following February.