At first, the SS killed prisoners by shooting them or giving them lethal injections in the camp's "hospital." Then, starting in 1942, they began sending prisoners to other places that did have gas chambers, like Hartheim Euthanasia Centre, so they could be killed there. Between 1942 and 1944, the SS sent about 60 groups of prisoners to Hartheim to be gassed to death. Each group had 60 to 1,000 prisoners in it.