The mandate of the Fourth Amendment requires adherence to judicial processes, and searches conducted outside the judicial process, without prior approval by judge or magistrate, are per se unreasonable under the Fourth Amendment, subject only to a few specifically established and well-delineated exceptions.
Petitioner, Katz, was convicted under an indictment charging him with transmitting wagering information by telephone across state lines. The evidence of petitioner's end of the conversations was introduced at the trial and obtained and overheard by FBI agents who had attached an electronic listening and recording device to the outside of the telephone booth from which the calls were made. The court convicted Katz, who appealed the conviction on the ground that the evidence entered at trial violated his Fourth Amendment. On appeal, the Court of Appeals affirmed the conviction, finding that there was no Fourth Amendment violation since there was "no physical entrance into the area occupied by" petitioner.
Did the Government’s eavesdropping activities violate the petitioner’s right against unreasonable search and seizure?
The Court held that the Government's eavesdropping activities violated the privacy upon which petitioner justifiably relied while using the telephone booth and thus constituted a "search and seizure" within the meaning of the Fourth Amendment. The Court further held that the Fourth Amendment governs not only the seizure of tangible items but extends as well to the recording of oral statements. The Court also opined that because the Fourth Amendment protects people rather than places, its reach cannot turn on the presence or absence of a physical intrusion into any given enclosure. Following these, the Court overturned the Court of Appeals’ ruling.