Himmler vs Canaris
The film highlights the rivalry between the leaders of two fiefdoms within the Third Reich. Admiral Canaris, the head of the German Intelligence and Heinrich Himmler, the boss of the SS. Himmler uses the idea of a plot to kidnap Winston Churchill as a way to score points against his rival and as a vehicle to please Adolf Hitler.
The letter of authorisation given to Colonel Radl by Himmler is clearly a forgery. Himmler wants the plan to succeed until it's apparent that its not going to work. He then has to cover his tracks so he has Radl arrested and killed. He knows that he has overstepped the mark and he has to cover his tracks.