They actually stopped in November 1944. Himmler, the head of the SS, who was in charge of the "final solution of the Jewish question", saw that Germany was going to lose the war and wanted to clean up his act to save his hide. In particular, he ordered the gas chambers and crematoria at Auschwitz completely dismantled and destroyed, so as to leave no evidence. A few months later he also began negotiating with Sweden for the release of camp inmates (mainly non-Jews and not from Auschwitz, which had been liberated by that time). About 15,000 were released in the last few months of the war.