Zyklon B
According to testimony of his superior Rudolf Höss, it was also Fritzsch who first came up with the idea of using poison gas Zyklon B for the purpose of mass murder. Fritzsch ordered the killing of Soviet POWs locked in cells in the basement of the Bunker while Höss went away on an official trip in late August 1941. Fritzsch tried out the effect of Zyklon B inside cells which were not air-tight, subjecting the victims to even more torturous death. Fritzsch repeated the test-killing of additional victims using Zyklon B soon thereafter in the presence of Höss. According to Höss the preferred method for the mass murders in Auschwitz using Zyklon B was devised on site.