A primary cause of death was illness due to harsh camp conditions, with starvation - and its consequent illnesses - prevalent. Malnourished and suffering from disease, many were literally "worked to death" under the Vernichtung durch Arbeit policy (extermination through labor), as inmates had only the choice between slave labour or inevitable execution. Many inmates died as a result of human experimentation or fell victim to arbitrary acts perpetrated by the SS guards. Other prisoners were simply murdered, primarily by shooting and hanging.