Answer:
Acting on a suspicion that Katz was transmitting gambling information over the phone to clients in other states, Federal agents attached an eavesdropping device to the outside of a public phone booth used by Katz. Based on recordings of his end of the conversations, Katz was convicted under an eight-count indictment for the illegal transmission of wagering information from Los Angeles to Boston and Miami. On appeal, Katz challenged his conviction arguing that the recordings could not be used as evidence against him. The Court of Appeals rejected this point, noting the absence of a physical intrusion into the phone booth itself. The Court granted certiorari.
