Complex sentence: The "Sonderkommando" in Auschwitz were mostly Jewish inmates and sometimes Russian prisoners-of-war who were forced to work in and around the gas chambers; they were first known as "Sonderkommando" in September 1942.
Split into simpler sentences: The "Sonderkommando" in Auschwitz were mostly Jewish inmates and sometimes Russian prisoners-of-war who were forced to work in and around the gas chambers. They were first known as "Sonderkommando" in September 1942.