The following link is to a youtube video and is a first hand account of Yisreal Gutman which was apart of a rebellion of a concentration camp. He explains his job was to get the wounded to a bunker. The conditions described are terrible and the battles that would occur in these camps contributed so much to the number of death in Jews.
http://www.youtube.com/watch?v=lQQkDjYoTN8
This video is a primary source of a trip to Auschwitz, the largest death/concentration camp. The camp was know for the terrible living conditions and the video captures materials that were actually used and thrown in a pile when needed to be disposed of the pile shows the numbers of those and the video describes that 1,100,000 people total were killed in the camp and the majority were Jews that died in gas chambers.