According to "British Intelligence in the Second World War: Security and Counter-Intelligence", by Francis Harry Hinsley and C.A.G. Simkins, Tricycle, a British double agent, complained that the FBI ignored the "obvious warning" of the forthcoming attack on Pearl Harbor (read more below ↓).
Also, according to "Conspiracies and Secret Societies: The Complete Dossier", by Brad Steiger & Sherry Steiger, it seems that the Japanese diplomatic code had been broken by FBI and almost all messages between Tokyo and its embassy in Washington were being intercepted and understood by Washington (read more below ↓).
Therefore, as it is possible to argue, there is no longer any doubt that FBI and, perhaps, Franklin Delano Roosevelt, were aware that an attack on Pearl Harbor was developing and that it was scheduled for December 7th.
Then a terrible question arises: was the attack on the American forces at Pearl Harbor totally unexpected?
If not, why did no one alert defense forces to protect Pearl Harbor?