From the establishment of Auschwitz concentration camp, the bodies of the prisoners murdered there were burned. The launch of the first crematorium in August 1940 workforce was needed to operate it. First Polish prisoners employed at the crematorium were not part of a special task force later known as Sonderkommando but were referred to as Krematorium Heizer (crematorium stokers). They were free to move within the camp and were not isolated from the rest of the prisoners. Moreover, they were given the same few rights as political prisoners.
With the increased Jewish population being sent and designated for extermination in 1942, the camp required a larger task force to operate the crematoria. SS decided to move the process of mass extermination to Birkenau camp adding Jewish prisoners to work at the crematorium. For the purpose of these special operations (Sonderaktionen), two more crematoria were built. Unlike the Polish prisoners, they were put in isolation from the rest of the prisoners. A constant increase of transports carrying Jews required even more workforce and a special work squad, Sonderkommando, was established.
Jewish prisoners forced to work for a Sonderkommando, Source: Wikipedia
The recruits of the Sonderkomanndo were young Jews between age 20 and 30, exclusively men from various countries of Europe chosen immediately upon arrival to the camp. One of the basic criteria for the prisoners selected for this task was physical strength since SS wanted the task carried out quickly and efficiently. By the instructions issued by the highest SS authorities, prisoners selected for the Sonderkommando were supposed to be executed after each extermination operation. However, Auschwitz SS authorities realized that prisoners who got used to this specific work performed better and the entirety of the Sonderkommando was terminated only once.
Prisoners assigned to the Sonderkommando were not able to refuse to do the work or ask to be transferred to perform another task. Failure to do the work assigned to them would result in immediate death. Personnel cards of Sonderkommando were in possession of Auschwitz Gestapo due to their status of Geheimnisträger (bearers of secrets) and their documentation almost non-existent after the war. The number of Sonderkommando prisoners was around 400 in 1942 and 1943, fell to 200 in early 1944 due to the failed attempt of an uprising of the Sonderkommando prisoners, and the highest number reaching 870 prisoners in mid-1944 with intensified deportation of Jews.
The work of the Sonderkommando prisoners was psychologically extremely demanding and physically exhausting. Their job was divided into maintenance and manual labor. Basic functions of the work related to the extermination included: undressing and leading the newly arrived prisoners to gas chambers called ‘the bathing’ and escorting disabled and restraining the nervous so they could be shot to death. Taking the belongings of the prisoners sent to the gas chambers. Cleaning the gas chambers of the feces from the bodies and searching for the hidden valuables. Transportation of the bodies and burning them in crematoria or outside burning pits.