The SS officer Werner Best, one-time head of legal affairs in the Gestapo, summed up this policy by saying, "As long as the police carries out the will of the leadership, it is acting legally". On 27 September 1939, the security and police agencies of Nazi Germany—with the exception of the Order Police—were consolidated into the Reich Main Security Office (RSHA), headed by Heydrich. The Gestapo became "Amt IV" (Department IV) of RSHA and Müller became the Gestapo Chief, with Heydrich as his immediate superior. After Heydrich's 1942 assassination, Himmler assumed the leadership of the RSHA until January 1943, when Ernst Kaltenbrunner was appointed chief. Müller remained the Gestapo Chief. His direct subordinate Adolf Eichmann headed the Gestapo's Office of Resettlement and then its Office of Jewish Affairs ("Referat IV B4" or Sub-Department IV, Section B4). During the Holocaust, Eichmann and his agency coordinated the mass deportation of European Jews to the Nazis' extermination camps. The power of the Gestapo included the use of what was called, "Schutzhaft"—"protective custody", a euphemism for the power to imprison people without judicial proceedings. An oddity of the system was that the prisoner had to sign his own "Schutzhaftbefehl", an order declaring that the person had requested imprisonment—presumably out of fear of personal harm. In addition, thousands of political prisoners throughout Germany—and from 1941, throughout the occupied territories under the Night and Fog Decree—simply disappeared while in Gestapo custody. The Polish government in exile in London during World War II received sensitive military information about Nazi Germany from agents and informants throughout Europe. After Germany conquered Poland in the autumn of 1939, Gestapo officials believed that they had neutralised Polish intelligence activities. However, certain Polish information about the movement of German police and SS units to the East during the German invasion of the Soviet Union in the autumn of 1941 was similar to information British intelligence secretly obtained through intercepting and decoding German police and SS messages sent by radio telegraphy. In 1942, the Gestapo discovered a cache of Polish intelligence documents in Prague and were surprised to see that Polish agents and informants had been gathering detailed military information and smuggling it out to London, via Budapest and Istanbul. The Poles identified and tracked German military trains to the Eastern front and identified four Order Police battalions sent to occupied areas of the Soviet Union in October 1941 that engaged in war crimes and mass murder.