In the 1959 case Rios v. United States, the U.S Supreme Court ruled on an issue of illegal search and seizure. The defendant, Rios, was arrested after a police officer observed him acting suspiciously in a parked car late at night. Upon approaching the vehicle, the officer saw what he believed to be narcotics and subsequently arrested Rios without first obtaining a warrant for either his arrest or for searching his vehicle. The court held that this constituted an unlawful search and seizure under the Fourth Amendment as there were no exigent circumstances justifying immediate action by law enforcement officers without securing a warrant first. Therefore, any evidence obtained from such searches could not be used against Rios in court proceedings due to its unconstitutional acquisition.

In the dissenting opinion for Rios v. United States, Justice Clark argued that the majority's decision undermined law enforcement efforts and contradicted established legal principles. He contended that police officers acted reasonably when they arrested Rios based on suspicious behavior and a reliable tip about drug trafficking. According to him, it was not necessary for officers to observe an actual crime or obtain a warrant before making an arrest in such circumstances. Furthermore, he disagreed with the majority's view that evidence obtained during this arrest should be excluded from trial as "fruit of the poisonous tree." Instead, he believed this doctrine should only apply when there is clear proof of police misconduct or violation of constitutional rights - which was not evident in this case.