How harshly should perpetrators of past abuses be punished, to reinforce the legitimacy of a new democracy? Drawing on sociopsychological theories, we hypothesize that prodemocratic mass attitudes are favored by the perception that defendants in transitional justice trials have been punished in a way that is morally proportional to their offenses. This perception is shaped by the social categorization of defendants and the opinions about the certainty of their guilt that predominate in the mass public. When defendants are largely seen as co-ethnics and their guilt is contested, like in the West German case, prodemocratic attitudes are likely to be strengthened by lighter punishments and undermined by harsher sanctions. The analysis of subnational variation in patterns of punishment in postwar West Germany confirms this hypothesis and shows that these attitudinal effects persist in the medium term. Our findings have implications for research on transitional justice and democratization.