About the Case

On August 4, 1944, after more than two years in hiding at the Prinsengracht 263 in Amsterdam, Fritz Pfeffer, the Van Pels and the Frank families were discovered. What led to the raid remains unclear to this day. Betrayal seemed to be the only logical conclusion, but by whom and why? Most investigations were done by writers, journalists and/or historians, but never by a team of forensic investigators using a wide variety of different techniques and expertise. Until now.

Police investigations

Upon returning from Auschwitz, Otto Frank discovered that he was the sole survivor of the group of eight people that went into hiding in the annex of his company, Opekta. His wife Edith, his two daughters Margot and Anne, Hermann and Auguste van Pels, their son Peter, and dentist Fritz Pfeffer had all perished in concentration camps in Germany and Poland.

Immediately after the war, Otto urged for an investigation into the arrest. An investigation by the Dutch police in 1947 led to no conclusive evidence against warehouse manager Van Maaren. A second police investigation in 1963 also exonerated the former employee. In subsequent years, Otto seemed to lose interest in finding the culprit.


Over the past 75 years, several people have attempted to solve the mystery of the raid. These attempts resulted in about thirty Persons of Interest. Could it have been one of the neighbours living near the annex? Could they have been enticed by rewards offered for turned-in Jews? Or could it have been the former employee, Job Jansen, who suspected Otto of having an affair with his wife Jetje?

In 1998, the Austrian journalist and writer Melissa Müller published a biography of Anne Frank. She suggested that the cleaning lady, Lena Hartog-van Bladeren, could have been the betrayer. She was the wife of the other warehouse worker at Opekta, Lammert Hartog.
In 2003, the British writer Carol Ann Lee published the biography of Otto Frank. In her research, she stumbled upon the possible blackmail of Otto Frank by a shady character named Tonny Ahlers. She suggested that he might have betrayed the people in the annex.
In 2010, another notable suspect was introduced, Ans van Dijk. She was a Jewish woman who was arrested and threatened with deportation. She became a successful agent for the Gestapo and responsible for dozens of betrayals. Her ‘success’ as a Jew hunter, as well as her overtly lesbian lifestyle, caused her to be the only woman to be executed after the war.
In 2016, the Anne Frank House published another theory on the raid. After a two-year study, they suggested that the discovery may have been a coincidence. The raiding party could have been looking for something else and stumbled upon the door to the annex by accident.

Cold Case Diary: Anne Frank

To this day, the mystery remains and many questions are left unanswered. But new sources can lead to new hypotheses. Retired FBI agent Vince Pankoke, war crime investigator Brandon Rogers, criminologist Monique Koemans and their investigation team bring a new perspective to the questions with Cold Case Dairy: Anne Frank. The truth about the raid of Anne Frank and the others is now being researched utilizing cold case investigative techniques that have only been developed in the past decades.

Artificial intelligence

Can big data help in the search on who betrayed the Secret Annex, leading to the raid on August 4, 1944?

Big data and Artificial Intelligence (AI) are relatively new research methods but they are growing at an incredibly speed. Specially developed software and AI – consulted by Amsterdam based big data company Xomnia and developed by the team of Microsoft – are used to organize and process the vast amount of data already collected, and this method has already generated new insights. It enables the team to see connections that are not always visible to the human eye.

The diary of a young girl, Anne Frank

Anne Frank was born in the German city of Frankfurt am Main in June of 1929. Anne, her parents, Otto and Edith, and her older sister, Margot, were forced to leave Germany because of the growing anti-Semitism in Germany after the rise of Adolf Hitler and his Nazi party. They fled to Amsterdam, the Netherlands, where Otto started a business, Opekta, on Prinsengracht 263. In May 1940, however, Nazi Germany invaded Holland and the family was yet again confronted with restrictive and discriminating laws. Anne and seven others spent over two years concealed in the annex of her father’s office building to avoid deportation to one of the camps. Tragically, they were discovered by the Gestapo.

Anne would not live to see the Allied liberation in 1945.
While in hiding the young girl kept a diary, beginning each entry with "Dear Kitty". She wrote about her daily life, feelings, and thoughts in a remarkably talented way, especially for a girl of her age. Anne’s diary was found after the raid by one of the helpers, Opekta’s secretary Miep Gies. Miep kept it, hoping to return it to Anne after the war. After Otto and Miep received news about Anne’s death, Otto decided to publish the diary, seeing it hit the shelves with the title Het Achterhuis in 1947. The English translation was published in 1952 under the title, Anne Frank: The Diary of a Young Girl. ‘Kitty’ would become an inspiration for millions of people around the world.