Furthermore, Milgram's research into variables affecting obedience has been criticised by Mandel. Milgram's research suggests that obedience decreases when the proximity between the learner and teacher increases because the teacher is seeing the direct impact of their actions. However, the mass killing of Jews in the holocaust was conducted in close proximity. Also, Milgram states that obedience increases due to the presence of uniforms but Mandel argues that this offers an excuse for evil behaviour, it is offensive to survivors to suggest that Nazis were victims of situational variables.