On 13 October 1941, SS and Police Leader Odilo Globočnik headquartered in Lublin received an oral order from Himmler – anticipating the fall of Moscow – to start immediate construction work on the first killing centre at Bełżec in the General Government territory of occupied Poland. Notably, the order preceded the Wannsee Conference by three months. The new camp was operational beginning 17 March 1942, with leadership brought in from Germany under the guise of Organisation Todt (OT). Each death camp was managed by between 20 and 35 officers from the "Totenkopfverbände" (Death's Head Units) sworn to absolute secrecy, and augmented by the "Aktion" T4 personnel selected by Globočnik. The extermination program was designed by them based on prior experience from the forced euthanasia centres. The bulk of the actual labour at each "final solution" camp was performed by up to 100 mostly Ukrainian Trawniki guards, recruited by SS-"Hauptsturmführer" Karl Streibel from among the Soviet prisoners of war, and by up to a thousand "Sonderkommando" prisoners whom the Trawniki guards used to terrorise. The "SS" called their volunteer guards "Hiwis", an abbreviation of "Hilfswillige" (lit. "willing to help"). According to the testimony of SS-"Oberführer" Arpad Wigand during his 1981 war crimes trial in Hamburg, only 25 percent of recruited collaborators could speak German.