Cold-case investigation names surprise suspect in Anne Frank's betrayal

The note said Van den Bergh had access to addresses where Jews were hiding as a member of Amsterdam's wartime Jewish Council and had passed lists of such addresses to the Nazis to save his own family.

Twisk said only four out of an initial 32 names remained following the research, with Van den Bergh the lead suspect.

Investigators confirmed that Otto, the only member of the family to survive the war, was aware of the note but chose never to speak of it publicly.

Van Twisk speculated that Frank's reasons to remain silent about the allegation were likely that he could not be sure it was true, that he would not want information to become public that could feed further anti-Semitism, and that he would not want Van den Bergh's three daughters to be blamed for something their father might have done.

Otto "had been in Auschwitz," Van Twisk said. "He knew that people in difficult situations sometimes do things that cannot be morally justified."

While other members of the Jewish Council were deported in 1943, Van den Bergh was able to remain in the Netherlands. He died in 1950.

Historian Erik Somers of the Dutch NIOD institute for war, holocaust and genocide studies praised the extensive investigation, but was skeptical of its conclusion.

He questioned the centrality of the anonymous note in the arguments for Van den Bergh's responsibility and said the team made assumptions about wartime Amsterdam Jewish institutions that are not supported by other historical research.

According to Somers there are many possible reasons Van den Bergh was never deported as "he was a very influential man."

Miep Gies, one of the family's helpers, kept Anne's diary safe until Otto returned and first published it in 1947. It has since been translated into 60 languages and captured the imagination of millions of readers worldwide.

The Anne Frank House Foundation was not involved in the cold case investigation but shared information from its archives to assist.

Director Ronald Leopold said the research had "generated important new information and a fascinating hypothesis that merits further research."

Using modern research techniques, a master database was compiled with lists of Dutch collaborators, informants, historic documents, police records and prior research to uncover new leads.

Dozens of scenarios and locations of suspects were visualized on a map to identify a betrayer, based on knowledge of the hiding place, motive and opportunity.

The findings of the new research will be published in a book by Canadian author Rosemary Sullivan, "The Betrayal of Anne Frank," which will be released on Tuesday.

The director of Dutch Jewish organization CIDI which combats anti-Semitism told Reuters she hoped the book would provide insight into the wartime circumstances of Amsterdam's Jewish population.

"If this turns into 'the Jews did it' that would be unfortunate. The Nazis were ultimately responsible," Hanna Luden of CIDI said.