In Lustig v. United States (1948), the U.S. Supreme Court ruled that evidence obtained illegally by a private party is inadmissible in court if law enforcement officials participated to any degree in the illegal action, even if they did not instigate it or participate directly. The case involved Jack Lustig who was convicted of possessing counterfeit money based on evidence found during an illegal search conducted by a hotel detective with police officers present but not actively participating. The Court held that because the police had engaged in what amounted to a joint operation with the hotel detective, they were as much responsible for his actions as he was and therefore, all evidence obtained from this search could be excluded under the exclusionary rule which prevents unlawfully seized items from being used at trial.

In the dissenting opinion for Lustig v. United States, Justice Frankfurter argued that the majority's decision blurred the line between federal and state law enforcement responsibilities. He contended that a search conducted by local police should not be considered a federal search merely because of subsequent collaboration or cooperation with federal agents. In his view, this interpretation could potentially allow for manipulation of constitutional protections against unreasonable searches and seizures by simply involving federal officers after an initial state-level investigation. Furthermore, he expressed concern about potential abuses if any evidence obtained through such collaborations were admissible in court under Federal rules even though they might have been obtained illegally under State laws.