For example, detailed lists of potential victims were made and maintained using Dehomag statistical machinery, and meticulous records of the killings were produced (for example, the precise counts of executed Jews in the Höfle Telegram). As prisoners entered the death camps, they were made to surrender all personal property to the Nazis, which was then precisely catalogued and tagged, and for which receipts were issued. In addition, considerable effort was expended over the course of the Holocaust to find increasingly efficient means of killing more people; for example, by switching from carbon monoxide poisoning in the Aktion Reinhard death camps of Belzec, Sobibór, and Treblinka to the use of Zyklon B at Majdanek and Auschwitz.
In his book Russia's War, British historian Richard Overy describes how the Nazis sought more efficient ways to kill people. In 1941, after occupying Belarus, they used mental patients from Minsk asylums as guinea pigs. Initially, they tried shooting them by having them stand one behind the other, so that several people could be killed with one bullet, but it was too slow. Then they tried dynamite, but few were killed and many were left wounded with hands and legs missing, so that the Germans had to finish them off with machine guns. In October 1941, in Mogilev, they tried the Gaswagen or "gas car". First they used a light military car, and it took more than 30 minutes for people to die. Then they used a larger truck exhaust and it took only eight minutes to kill all the people inside.
Alleged corporate involvement in the Holocaust has created significant controversy in recent years. Rudolf Hoess, Auschwitz camp commandant, said that far from having to advertise their slave labour services, the concentration camps were actually approached by various large German businesses, some of which are still in existence. Technology developed by IBM also played a role in the categorization of prisoners, through the use of index machines.
