Most Jewish men who were sent to Treblinka were killed right away. However, a few were chosen to be its slave-labor units, called "Sonderkommando." When the Nazis murdered people in the gas chambers, they forced the "Sonderkommando" to bury the victims' bodies in mass graves. These bodies were exhumed in 1943 and cremated on large open-air pyres, along with the bodies of new victims. 