This study investigated the impact of jailhouse informant testimony on mock juries. In addition to allowing for jury deliberations, individual judgments (as measured in most prior research) were examined. Two hundred ninety-one undergraduates, in five to six-member mock juries, heard a fictional murder trial summary in one of three conditions: jailhouse informant testified after receiving an incentive, jailhouse informant testified after receiving no incentive, or no jailhouse informant testimony. Participants made predeliberation judgments, deliberated on a verdict, and made postdeliberation judgments. The primary results showed that there were more guilty verdicts for juries that heard jailhouseinformant testimony than for those that did not hear such testimony. This relationship was fully mediated by perceptions of the defendant (e.g., sympathy for and credibility of). In addition, jury deliberations often produced a change in verdict; those who gave an initial guilty verdict were more likely to switch to not guilty after deliberation. Finally, cognitive network analyses showed that jailhouse informant testimony was the focus of jury deliberations for both guilty (viewed the testimony as reliable) and not guilty (viewed the testimony as unreliable) verdicts. Results are discussed in terms of the importance of how jailhouse informant testimony can influence jury deliberations in both a positive and negative way.