BRUSSELS – Has a painful 70-year-old mystery been solved? A book published Tuesday claims that new evidence points to the informer who led to the capture of Anne Frank and her family by the Nazis in 1944 being Nelly Voskuijl, the sister of Elisabeth “Bep” Voskuijl, who helped the Franks in their hideout.

The book, a biography dedicated to Bep, was written by Flemish journalist Jeroen de Bruyn together with Elisabeth’s youngest son, Joop van Wijk. Their conclusions are based, among other things, on the testimony of two people who at the time refused to tell what they knew, for understandable reasons: the third sister, Diny, and Bep’s fiancé during the war, Bertus Hulsman.

The authors were able to find proof that Nelly, her younger sister, who passed away in 2001, collaborated with the Gestapo in occupied Holland when she was aged 19 to 23. “Our conclusion is painful, but clear,” note the authors.

They say that they also discovered that at the time, when the Franks found a hiding place in Amsterdam, Nelly was angry that her sister Elisabeth and her father Johan – the two who knew about the attempt to save Anne and her family – were sympathetic toward the Jews. Members of her family said that on one occasion she said to them angrily: “Go, then, go to your Jews.”

The circumstantial evidence found by the authors includes the fact that Karl Silberbauer, the Austrian SS officer who was responsible for the arrest of the Franks, claimed when he was found in 1963 that the information was given in “the voice of a young woman.” Nelly was 21 years old at the time.

Bep Voskuijl worked before the war in the Dutch office of Opekta, one of the businesses run by Otto Frank, Anne’s father. In 1942 she also became the administrative director of the firm. During the entire time they found refuge in the hideout, she helped them and brought them food and clothing. It was her father who installed the famous “library door” that concealed the Franks’ hiding place.

Bep suspected her sister all along, but kept quiet until her dying day in 1983.

The mystery of the informant has always hovered over the Anne Frank story. The initial suspicion at the time fell on Willem van Maaren, the cleaning man in the warehouse adjacent to the house where the hideout was located. But he was acquitted after a trial in 1949.

In the late 1990s, a study by Austrian historian Melissa Müller claimed that the informant was a young woman named Lena Herzog, also a cleaning woman in the same warehouse. But her version was rejected by everyone involved in the story at the time.