In Brown v. Illinois (1974), the U.S. Supreme Court ruled that a confession obtained from an individual who was arrested illegally cannot be used as evidence in court, even if it is voluntarily given after being read their Miranda rights. The case involved Richard Brown, who had been arrested without probable cause and later confessed to murder while in police custody. The Court held that the confession could not be admitted into evidence because it was "fruit of the poisonous tree," meaning it resulted directly from an illegal action by law enforcement officers - his unlawful arrest. This decision reinforced the Fourth Amendment's protection against unreasonable searches and seizures, emphasizing that such protections extend beyond physical property to include individuals' statements or confessions.

In the dissenting opinion for Brown v. Illinois, Justice William H. Rehnquist argued that the majority's decision to suppress evidence obtained after an illegal arrest was misguided and overly broad in its interpretation of the Fourth Amendment. He contended that there should be a more flexible approach when determining whether confessions made following unlawful arrests are admissible as evidence or not, rather than automatically excluding them based on procedural errors during arrest. The justice believed this would allow for consideration of factors such as voluntary nature of confession and time elapsed between arrest and confession which could potentially validate their use in court proceedings despite initial illegality of detainment. He feared that by adopting a strict exclusionary rule, it might inadvertently encourage criminals to commit offenses with impunity knowing any subsequent incriminating statements they make will be discarded due to technicalities related to their apprehension.