Retired FBI agent has new theory about who betrayed Anne Frank’s family to Nazis 6 hours ago arstechnica.com Enlarge / Anne Frank in 1940. A new book, The Betrayal of Anne Frank: A Cold Case Investigation , by Rosemary Sullivan, claims that a retired FBI special agent and a team of investigators have solved the mystery of who betrayed the Frank family to the Nazis. Enlarge / A model of the building where Anne Frank stayed, including the Secret Annex Enlarge / A reproduction of Anne Frank's diary, part of a permanent exhibition about the life of Anne Frank at...