When were the Nazi concentration camps discovered?

1. The existence of concentration camps (punishment and labour camps) was well known already in 1933. One of their key functions at that time was to deter anyone thinking of opposing the Nazis. The existence of camps such as Dachau was never a secret, though precise details of what happened in these camps were not so well known. 2. Information about the existence of extermination camps reached the Allies from December 1941 onwards, but they were very skeptical about the information until mid 1944. 3. On 22 July 1944 the Soviet Army liberated Majdanek - the first major camp to be reached by any of the Allies.