10 Strangest World War II Unsolved Mysteries

1. Who Turned Anne Frank In?

Everyone knows the tragic story of Anne Frank - the German Jew who was captured and killed during the Holocaust at Bergen-Belsen Concentration Camp, but not before she wrote a diary while in hiding in Amsterdam that came to light in July 1945.

From her family, only her father, Otto Frank, survived the war - and this tragic tale has asked an important question ever since: Who made the anonymous phone call that told the Gestapo about their hiding place in a secret annex (or "Achterhuis") above the so-called "Anne Frank House" and shopped them? Various suspects have been suggested over the years - with the most-often blamed being Willem van Maaren, who was a warehouse manager.

When allegations were made towards Van Maaren, however, all potential witnesses had died - including Julius Dettman the Nazi officer who received the phone call. Another suspect is long-time friend of Otto Frank, Tonny Ahlers. Ahlers' son Anton helped in the creation of a biography of Otto Frank in 2002, and he claimed his father had indeed reported the family to the Gestapo. Lena Hartog-van Bladeren, a cleaning lady, may also have turned over the family because she feared her husband would be arrested and she is known to have testified that Jews had lived in the property.

In addition, other employees in the warehouse that became "Anne Frank House" also revealed in a 1948 investigation that they knew the family were hidden in the secret annex - meaning they are certainly suspects as well. Dettman committed suicide in the immediate aftermath of Germany's surrender, meaning that no conclusive proof could ever be found as to who made the phone call. The person who betrayed Anne Frank and her family will almost certainly never be determined, it seems.