There were many different ways to kill prisoners in a concentration camp and at first gassing was not needed. But as more and more prisoners were transported to the camp, it became necessary. In the Mauthausen chamber, they could murder 120 people at one time and it seems that as many as 10,000 prisoners were gassed in this room between 1942 and 1945. In the center of this picture, inside the room, you can see one of the several "shower heads".