In a recent Colorado case, a Colorado trial court allowed a jury to here testimony from two woman who said that they had been sexually assaulted by the defendant in a case involving a third woman, even though the two prior cases had gone to trial and resulted in acquittals. The judge found by a preponderance of the evidence that the sexual assaults had taken place despite the acquittals, and offered the women's testimony as modus operandi evidence (Colorado Rule of Evidence 404(b)). This decision was affirmed in a 2-1 decision, on appeal.
Given that their testimony, which provides trials within trials, in effect, could not be a complete as the actual trials that produced the acquittals, and the fact that the jury wanted that additional evidence and asked for it in deliberation, excluding the fact of the acquittals seems particularly prejudicial. Yes, acquittal does not mean a finding of innocence, and the jury should be instructed of this fact, but given the general distrust the legal systems has of propensity evidence, it should come with footnotes when appropriate to impeach the implication left, which was that the individual was a serial rapist with two prior convictions, something that wasn't the case.