In the 1991 case of Diane Griffin v. United States, the Supreme Court ruled on whether a jury must unanimously agree not only that an offense was committed but also about which specific act constituted the offense. The case involved Diane Griffin who had been convicted for mail fraud after she sent out five fraudulent mailings. While all jurors agreed that she had committed fraud, they could not reach consensus on which particular mailing constituted the crime. In a unanimous decision, the Supreme Court held that unanimity is required only in determining guilt or innocence of charges as a whole and it's unnecessary to agree upon exactly what acts constitute those crimes. Therefore, even though there was disagreement over which specific act led to her conviction for mail fraud, since all jurors agreed she had indeed committed this crime overall - her conviction stood.

In the dissenting opinion for Diane Griffin v. United States, 1991, Justice Marshall argued that the majority's decision to uphold a conviction based on an uncorroborated confession was fundamentally flawed. He contended that it contradicted long-standing legal principles requiring independent evidence to corroborate confessions before they can be used as grounds for conviction. According to him, this rule is essential in preventing wrongful convictions based on false confessions and ensuring fairness in criminal proceedings. Furthermore, he expressed concern about the potential misuse of power by law enforcement officials who might coerce or manipulate suspects into confessing crimes they did not commit without any need for additional proof of guilt. Therefore, he disagreed with the majority's ruling and believed that Griffin’s conviction should have been overturned due to lack of corroboration.