How does witnessing regime atrocities influence the political attitudes of bystanders? We argue that observing regime agents targeting vulnerable groups causes a psychological dissonance between individuals' sense of regime legitimacy and the observed moral transgression. As a result, regime support should decrease among witnesses of regime atrocities. To test this hypothesis, we analyze original, highly disaggregated archival data from the so-called Nazi "Death Marches'' at the end of World War II. In contrast to the Nazis' crimes inside the concentration camps, the death marches confronted ordinary German citizens with the regime's mass violence. We find that municipalities exposed to a high number of deaths display a lower vote share for post-WWII right-wing nationalist parties. In line with our proposed mechanism, we show that (1) this effect is particularly visible in time periods when Nazi crimes were politically salient in post-WWII Germany and (2) that death march exposure is associated with psychological and social disengagement in historical survey data. Our findings have implications for the durability of authoritarian regimes and democratization prospects.