In the United States v. Leon et al., 1983, the Supreme Court ruled on whether evidence obtained in violation of the Fourth Amendment could be used in court if police officers acted in good faith and with a warrant they believed to be valid. The case arose when Burbank Police Department officers conducted a search based on a warrant later deemed invalid due to lack of probable cause. The defendants moved to suppress the seized evidence under the exclusionary rule, which typically bars admission of such evidence. However, by a 6-3 majority decision, Justice Byron White writing for the court held that there was an exception to this rule: when law enforcement acts on good faith reliance upon a defective search warrant; henceforth known as "the Good Faith Exception". This ruling significantly modified previous interpretations of Fourth Amendment rights against unreasonable searches and seizures.

In the dissenting opinion for United States v. Leon et al., Justice Brennan, joined by Justice Marshall, argued that the majority's decision to create a "good faith" exception to the exclusionary rule undermined Fourth Amendment protections against unreasonable searches and seizures. They contended that this new exception would discourage law enforcement from ensuring they have proper legal basis before conducting a search or seizure. The justices also expressed concern about leaving it up to individual officers' subjective beliefs about what constitutes probable cause, which could lead to abuses of power and violations of citizens' rights. Furthermore, they disagreed with the majority's assertion that excluding evidence obtained through unlawful searches does not deter police misconduct; on contrary, they believed it is one of few effective deterrents available in such cases.