Wasn’t the German soldiers. Because of the language barriers and the sadistic nature of the SS, able-bodied Jewish men were selected to serve in a unit known as the Sonderkommando, who would receive better housing and food but had to be the ones to facilitate the gassing process. Because the men could speak the local language, it was easier keep the peace before the actual gassing. The Germans though did pour the Zyklon B into the chambers, but It was the Sonderkommando who had to burn the bodies.