from the age of 19 to 23. She had run away to Austria with a Nazi officer, and returned to Amsterdam in 1943 after the relationship ended. Nelly had been critical of Bep and their father, Johannes Voskuijl, for helping the Jews; Johannes was the one who constructed the bookcase covering the entrance to the hiding place and remained as an unofficial watchman of the hideout. In one of their quarrels, Nelly shouted to them, "Go to your Jews." Karl Josef Silberbauer, the SS officer who made the arrest, was reported to have said that the informer had "the voice of a young woman". In 2016, the Anne Frank House published new research pointing to an investigation over ration card fraud, rather than betrayal, as a possible explanation for the raid that led to the arrest of the Franks. The report stated that other activities in the building may have led authorities there, including activities of Frank's company; however, it did not rule out betrayal. In January 2022, some investigators proposed Arnold van den Bergh, a member of Amsterdam's Jewish Council who died in 1950, as the suspected informant. The investigators postulated that van den Bergh gave up the Franks to save his family. The investigation is chronicled in Rosemary Sullivan's book, The Betrayal of Anne Frank: A Cold Case Investigation. Evidence was also claimed to have been found that Anne Frank's father later knew this but did not reveal it after the war. According to the BBC, these investigators "spend six years using modern investigative techniques to crack the 'cold case…'." However, according to The New York Times, several World War II and Holocaust scholars have doubted the methods and conclusion of the investigation, calling the evidence "far too thin". Shortly after the publication of The Betrayal of Anne Frank, after criticism from scholars Bart van der Boom, David Barnouw and Johannes Houwink ten Cate, publisher Ambo Anthos, via an internal email, apologized for the publication of the Dutch translation. They said they should have been more critical and announced that they are "await(ing) the answers from the researchers to the questions that have emerged and are delaying the decision to print another run". In response, Pieter van Twisk, one of the investigators used in the book, said that he was "perplexed by the email" and that the investigators had never claimed to have uncovered the complete truth. In