In the case of Harris v. United States, the Supreme Court ruled in 1958 that evidence obtained through a warrantless search could be used to convict an individual if it was discovered while police were conducting another lawful activity. The case involved petitioner James Edward Harris who had been convicted for possessing forged money orders which were found during a search for other items related to different crimes he was suspected of committing. The court held that since officers had lawfully entered his home with an arrest warrant and only then stumbled upon the incriminating evidence "in plain view," their actions did not violate Fourth Amendment protections against unreasonable searches and seizures. This decision established what is known as the "plain view doctrine" in U.S criminal law, allowing police to seize without a warrant any illegal contraband or evidence they inadvertently come across while carrying out legal duties.

In the dissenting opinion for Harris v. United States, Justice Brennan disagreed with the majority's decision to uphold a conviction based on evidence obtained through an illegal search and seizure. He argued that this violated the Fourth Amendment rights of the defendant, which protect against unreasonable searches and seizures. Brennan contended that allowing such evidence would undermine these constitutional protections by incentivizing law enforcement officers to conduct unlawful searches in hopes of finding incriminating evidence. He also expressed concern about potential abuses of power if police were allowed to violate individuals' privacy rights without consequence or oversight from courts.