Top 10 Cases for Police Series, Part 9

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Editor's Note: With so many cases affecting policing, the question often arises regarding which are the most important. If a law enforcement professional could choose only 10 cases to examine, which would those be? Included in this series is a list of what experts Rolando del Carmen and Jeffery Walker consider to be the top 10 cases most influencing day-to-day policing in the U.S. Continuing from our last installment, in reverse order, we give you number 2: Mapp v. Ohio, 367 U.S. 643 (1961).


The exclusionary rule applies to all state criminal proceedings.


Mapp was convicted of possession of lewd and lascivious books, pictures, and photographs in violation of Ohio law. Three Cleveland police officers went to Mapp’s residence based on information that a person who was wanted in connection with a recent bombing was hiding out in her home. The officers knocked on the door and demanded entrance, but Mapp, telephoning her attorney, refused to admit them without a warrant. The officers again sought entrance three hours later, after the arrival of more police. When Mapp did not respond, the officers broke the door open. Mapp’s attorney arrived but was denied access to his client. Mapp demanded to see the search warrant the police claimed to possess. When a paper supposed to be the warrant was held up by one of the officers, Mapp grabbed the paper and placed it in her bosom. A struggle ensued and the paper was recovered after Mapp was handcuffed for being belligerent. A search of the house produced a trunk that contained obscene materials. The materials were admitted into evidence at the trial and Mapp was convicted of possession of obscene materials.


Is evidence obtained in violation of the Fourth Amendment protection from unreasonable searches and seizures admissible in state criminal prosecutions? NO.

Supreme Court Decision

The exclusionary rule, applicable in federal cases, which prohibits the use of evidence obtained as a result of unreasonable searches and seizures, also applies to state criminal proceedings.


“Since the Fourth Amendment’s right of privacy has been declared enforceable against the States through the Due Process Clause of the Fourteenth [Amendment], it is enforceable against them by the same sanction of exclusion as is used against the Federal Government. Were it otherwise, then just as without the Weeks rule the assurance against unreasonable searches and seizures would be ‘a form of words,’ valueless and undeserving of mention in a perpetual charter of inestimable human liberties, so too, without that rule the freedom from state invasions of privacy would be . . . ephemeral . . .”

Case Significance

Mapp is significant because the Court held that the exclusionary rule was thereafter to be applied to all states, thus forbidding both state and federal courts from accepting evidence obtained in violation of the constitutional protection against unreasonable searches and seizures. In the mind of the Court, the facts in Mapp illustrate what can happen if police conduct is not restricted. Mapp was therefore an ideal case for the Court to use in settling an issue that had to be addressed: whether the exclusionary rule should apply to state criminal proceedings. The Court answered with a definite yes.

For many more cases, see Briefs of Leading Cases in Law Enforcement, 8th ed., which includes short, easy-to-understand briefs of 185 cases of primary importance to law enforcement officials.


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