Mental health evidence concerning antisocial and psychopathic traits appears to be introduced frequently in capital murder trials in the United States to argue that defendants are a "continuing threat" to society and thus worthy of execution. Using a simulation design, the present research examined how layperson perceptions of the psychopathic traits exhibited by a capital defendant would impact their attitudes about whether he should receive a death sentence. Across three studies (total N = 362), ratings of a defendant's perceived level of psychopathy strongly predicted support for executing him. The vast majority of the predictive utility was attributable to interpersonal and affective traits historically associated with psychopathy rather than traits associated with a criminal and socially deviant lifestyle. A defendant's perceived lack of remorse in particular was influential, although perceptions of grandiose self-worth and a manipulative interpersonal style also contributed incrementally to support for a death sentence. These results highlight how attributions regarding socially undesirable personality traits can have a pronounced negative impact on layperson attitudes toward persons who are perceived to exhibit these characteristics.