ABSTRACT
When the U.S. Supreme Court mandated in Mapp v. Ohio, 367 U.S. 643 (1961), that states apply the exclusionary rule as the remedy for Fourth Amendment violations, the police found themselves in untenable circumstances. Courts quickly extended the Mapp rule regarding searches of residences to searches of individuals in public places. Although the police were required to deter and detect crime, they could no longer rely on the customary practices of stopping, questioning, and searching people at will. New and extraordinary restrictions were placed on their abilities to conduct investigations and to employ crime-prevention tactics. At the same time these restrictions were being imposed, crime was increasing drastically, especially in large cities where much of the population was transient. Often in crowded urban areas, the police did not know the identities of most of the people they encountered unless they stopped and questioned them, yet the courts held that to stop individuals and restrain their movements long enough to question them constituted an arrest. To arrest or even detain, the police needed probable cause:
The basic principles were relatively simple and straightforward. The term “arrest” was synonymous with those seizures governed by the Fourth Amendment. While warrants were not required in all circumstances, the requirement of probable cause, as elaborated in numerous precedents, was treated as absolute.1
