Demonstrations of a link between genetic variants and criminal behavior have stimulated increasing use of genetic evidence to reduce perceptions of defendants' responsibility for criminal behavior and to mitigate punishment. However, because only limited data exist regarding the impact of such evidence on decision makers and the public at large, we recruited a representative sample of the U.S. adult population (N = 960) for a Web-based survey. Participants were presented with descriptions of 3 legal cases and were asked to determine the length of incarceration for a convicted murderer, adjudicate an insanity defense, and decide whether a defendant should receive the death penalty. A fully crossed, between-participants factorial design was used, varying the type of evidence (none, genetic, neuroimaging, both), heinousness of the crime, and past criminal record, with sentence or verdict as the primary outcome. Also assessed were participants' apprehension of the defendant, belief in free will, political ideology, and genetic knowledge. Across all 3 cases, genetic evidence had no significant effects on outcomes. Neuroimaging data showed an inconsistent effect in 1 of the 2 cases in which it was introduced. In contrast, heinousness of the crime and past criminal record were strongly related to participants' decisions. Moreover, participants' beliefs about the controllability of criminal behavior and their political orientations were significantly associated with their choices. Our findings suggest that neither hopes that genetic evidence will modify judgments of culpability and punishment nor fears about the impact of genetic evidence on decision makers are likely to come to fruition.