In the 1992 case of Gloria Zafiro, Jose Martinez, Salvador Garcia and Alfonso Soto v. United States, the Supreme Court ruled on whether a jury could be instructed that they may infer guilt from one defendant based on evidence against another. The four defendants were charged with conspiracy to distribute cocaine; during their trial, the prosecution presented strong evidence against three of them but weaker evidence against Zafiro. The District Court gave an instruction known as a "spillover" or "interdependence" instruction which allowed jurors to consider each piece of evidence in relation to all defendants involved in the alleged conspiracy. On appeal, this was challenged as prejudicial towards Zafiro due to her lesser involvement. The Supreme Court held that such instructions are not inherently prejudicial and can be given if appropriate under specific circumstances - however it should not encourage conviction based solely on association with guilty parties. They found no reversible error in this case because there was substantial independent evidence implicating each defendant individually.

In the dissenting opinion for Zafiro v. United States, Justice Stevens argued that the majority's decision to allow separate trials only in cases where there is a serious risk of prejudice undermines the fairness and efficiency of joint trials. He contended that this standard was too high and would result in fewer defendants receiving separate trials than should be granted under Rule 14 of Federal Rules of Criminal Procedure. According to him, if there is any reasonable possibility that a defendant’s rights will be prejudiced by a joint trial, then severance should be granted as it ensures fair treatment for all parties involved. Furthermore, he expressed concern about potential conflicts between co-defendants' defense strategies which could lead to unfair outcomes if not addressed through separate proceedings.