People who report greater belief in pure evil (BPE; the tendency to attribute harmdoing to dispositionally sadistic perpetrators) generally punish criminal perpetrators more regardless of mitigating circumstances (e.g., having a brain tumor). What attributional/cognitive processes underlie such punishment? A national sample (final N = 302) read an alleged "USA Today" article about a mall shooting. We manipulated whether the shooter exhibited a brain tumor and whether the shooter exhibited stereotypically evil traits. Regardless of experimental conditions, individuals who reported greater BPE perceived the shooter's behavior as more internal, intentional, controllable, and blameworthy. These attributional judgments also helped mediate the relationship between BPE and punishment. Ancillary measures demonstrated other potential cognitive biases (overprecision and confirmation bias) in processing information about the shooter/shooting. In sum, people who report greater BPE held the shooter more liable for his actions despite mitigating evidence, and such attributions helped explain the link between BPE and punishment.