In the 1987 case Murray v. United States, the Supreme Court ruled on a matter concerning the Fourth Amendment's exclusionary rule, which prevents evidence obtained illegally from being used in court. The police had conducted an initial illegal search of a warehouse suspected to contain drugs and then later performed a second search after obtaining a warrant based on information unrelated to their first entry. The question was whether or not evidence found during this second legal search should be excluded because it might have been discovered during the earlier illegal one. In its decision, the Supreme Court held that if officers independently acquire information leading them to conduct an otherwise legal search (i.e., with probable cause and/or proper warrants), any evidence seized can be admitted into court even if there was prior illegal activity by law enforcement - as long as that unlawful action did not lead directly to obtaining either the incriminating evidence or warrant itself.

In the dissenting opinion for Murray v. United States, Justice Thurgood Marshall argued that the majority's decision undermined Fourth Amendment protections against unreasonable searches and seizures. He contended that allowing evidence obtained from an illegal search to be used in court because it was later re-obtained through a legal search creates a dangerous loophole in constitutional rights. This could potentially incentivize law enforcement officers to conduct unlawful searches with the hope of finding incriminating evidence, then securing warrants after-the-fact based on other information to legitimize their findings. Marshall believed this ruling blurred the line between lawful and unlawful police practices, eroding citizens' privacy rights and weakening necessary checks on police power.