College students (N= 270) assigned to six-person mock juries read summaries of a murder trial and then evaluated the defendant's guilt both before and after group discussion. The strength of the prosecution's case was manipulated, as was the inclusion of extra wiretapping evidence that favored the prosecution or the defense and was ruled admissible or inadmissible by the judge. Whether it favored the prosecution or the defense, inadmissible evidence directly biased subjects' reactions toward the defendant and indirectly biased their behaviors during the group discussions. None of these effects varied with the strength of the prosecution's case. The results also showed that the direct effects of inadmissible evidence were at least partially mediated by its indirect effects, suggesting that the process of deliberation can potentially help jurors to control the influence of inadmissible evidence on their decisions.