In the United States v. McMahon case of 1896, the Supreme Court ruled on a matter involving tax evasion and alcohol distillation. The defendant, McMahon, was accused of operating an illegal whiskey distillery and failing to pay taxes on his product. He argued that he had been unlawfully entrapped by a government agent who encouraged him to commit these crimes so they could arrest him for it later. However, the court rejected this argument stating that entrapment only applies when someone is induced into committing a crime they would not have otherwise committed if not for the persuasion from law enforcement officials or agents acting in their behalf. In this case, there was no evidence suggesting that McMahon wouldn't have engaged in illegal activities without encouragement from federal officers; thus ruling against him.

The dissenting opinion in the United States v. McMahon case argued that the majority's decision to uphold McMahon's conviction was flawed due to a lack of evidence proving his guilt beyond reasonable doubt. The dissenters believed that there were significant inconsistencies and contradictions in the testimonies provided by government witnesses, which raised doubts about their credibility and reliability. They also pointed out that some key pieces of evidence used against McMahon were circumstantial at best, making it difficult to conclusively link him with any criminal activities as charged by the prosecution. Furthermore, they criticized how certain procedural aspects of the trial had been handled, suggesting potential bias or unfairness towards McMahon during court proceedings. Overall, these justices felt strongly that upholding such a questionable conviction would set a dangerous precedent for future cases where defendants could be found guilty based on insufficient or unreliable evidence.