The BBC made a documentary about WWII, and one episode was about the death camps. A Jewish man who had been an inmate and a guard (the Nazis selected some inmates to serve as guards, called "Sonderkommandos", and these men received extra rations and even some weapons to use on the inmates under their command) was interviewed. He told horrible stories about inmates killing one another to get an extra crust of bread or bowl of gruel. He said something that stuck with me.