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In Mapp v. Ohio, the U.S. Supreme Court extended the due process protections of the exclusionary rule to include all "constitutionally unreasonable searches" that were done without a basis of probable cause. In the seven years after Mapp, when homicide rates in the U.S. nearly doubled, riots broke out in at least forty-seven U.S. cities. During the same era, a heroin epidemic gripped the nation's urban centers, giving rise to street drug markets and associated violence and pressures on law enforcement to curb those markets. As violence increased, a turn in the nation's political culture questioned Mapp's restraints on police discretion to stop and search criminal suspects. Indeed, some writers wondered if the Mapp standard, with its reliance on the exclusionary rule to deter violations of Fourth Amendment rights, had inflicted social costs on the public through over-deterrence of police, leading to elevated crime rates.

It was no surprise, then, that after those seven years the Supreme Court in Terry v. Ohio "uncoupled … the two clauses of the Fourth Amendment" that regulated temporary detentions and searches by police. Terry dealt with a different "rubric of police conduct": the beat officer stopping and patting down an individual on the street, more commonly known as an "investigative stop." The Terry test was (and is) thus to balance the scope of the intrusion against the "specific and articulable facts which, taken together with rational inferences from those facts, reasonably warrant [the] intrusion." Justice Douglas, in dissent, labeled this "reasonable suspicion." Although intended to be a narrow departure from Mapp's standard, it was in fact a big break from Mapp. The Court said that the Mapp rule simply did not fit the realities of street policing in an era of rising crime rates.


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