Penal Code section 954 provides for severance of separate criminal charges joined for trial. To successfully challenge the denial of a severance motion, an appellant must make a clear showing of prejudice and that the denial falls outside the bounds of reason. Under section 954, the prosecutor may combine multiple charges in a single pleading for trial if the charges are connected in their commission, or are different statements of the same offense, or belong to the same class of offenses. In evaluating a severance motion, the court’s key inquiry is whether joint trials pose an unacceptable risk of prejudice from the “spillover effect,” i.e., the risk that evidence not admissible as to one of the charges, but admitted in connection with the other, will affect the verdict on the charges as to which it is inadmissible. Evidence as to one offense may be cross-admissible for the purpose of establishing intent, motive, identity, or propensity in a separate offense. If it is determined that the evidence of one offense is not cross-admissible to the separate offense and, thus, results in a spill-over effect, it must then be determined if it prejudicially affected the jury’s assessment of the separate offense. In non-capital cases, this will require a determination as to whether the spillover evidence was likely to inflame the jury against the defendant and the extent to which it made a weak case stronger. Here, appellant was charged with indecent exposure and sexual assault. His motion to sever the two offenses for trial was denied and he was convicted of both of them. The crimes occurred three months apart, at different locations, different times of the day, and involved different conduct. The identity of appellant as the suspect in the indecent exposure offense was very strong whereas the identity of the suspect in the assault was weak. On this evidence, the appellate court ruled that there was no cross-admissibility and the trial court erred in permitting the prosecutor to conduct joint trials. Because the indecent exposure played a central role in the prosecutor’s case with the prosecutor presenting a variety of spurious legal theories to place evidence of the indecent exposure before the jury as evidence of the assault, the trial was grossly unfair and the appellate court reversed the assault conviction.