The "Sonderkommando" ("Special commando") was a group of male inmates, who were already sentenced to death by committing them into that commando. Since the SS wanted to avoid witnesses of their horrible crimes, they also killed the members of the "Sonderkommando" at regular intervals.
The "Sonderkommando" had to "help" the SS, when prisoners undressed before entering the gas chamber, it had to convey the bodies from the gas chambers to the crematory ovens or to pile them, burn them and get rid of the ashes. Sometimes it happened that members of that "Sonderkommando" met family members and had to help killing them.
After the gassing, the "Sonderkommando" also had to clean the gas chamber and sort the remains of the dead people, such as their clothes. Prisoners physicians who belonged to the "Sonderkommando", too, removed golden teeth from the bodies.
The "Sonderkommando" was strictly isolated from other inmates. The prisoners were not allowed to have any contact with members of that commando.
The influence of the work within the "Sonderkommando" was pernicious to its members: They became hardened, lost any feeling, their physiognomy changed that much, that they looked very much alike in their brutal appearance.
"Greenhorns" in the "Sonderkommando" often broke down psychically when they became aware of what they did. The consequence was refusal to work. They voluntarily jumped into the gas chamber or into the SS-guards in order to be shot, just because they wanted to escape their horrible destiny.