The U.S. Supreme Court case O'Neal v. United States in 1902 revolved around the issue of whether a person could be convicted for conspiracy to defraud the federal government based on evidence that they had conspired to counterfeit money, even if no actual counterfeiting took place. The defendant, O'Neal, argued that since no counterfeit money was ever produced or circulated as part of his alleged conspiracy, he could not be guilty of conspiring to defraud the United States. However, the court disagreed and upheld his conviction. It ruled that it was enough for a person to have agreed with others to commit an unlawful act against the government - in this case counterfeiting - regardless of whether or not they succeeded in carrying out their plan.

In the dissenting opinion for O'Neal v. United States, it was argued that the majority's decision to uphold a conviction based on evidence obtained through an unlawful search and seizure violated the Fourth Amendment rights of the defendant. The dissent contended that by allowing such evidence to be used in court, it effectively condoned illegal actions by law enforcement officials. It further asserted that this ruling undermined citizens' constitutional protections against unreasonable searches and seizures, setting a dangerous precedent for future cases. The dissent also expressed concerns about potential abuses of power by police officers who might feel emboldened to conduct warrantless searches with impunity knowing any incriminating evidence they find could still be admissible in court despite being illegally obtained.