Carroll v. United States

The Fourth Amendment prohibits unreasonable searches and seizures, not every search or seizure conducted without a warrant. Its meaning must be informed by the practices understood as permissible when the Amendment was adopted, while also protecting both public interests and individual rights.

The Court distinguished searches of homes and other fixed structures from searches of movable vehicles. A warrant can ordinarily be obtained before searching a dwelling or building, but an automobile can quickly leave the locality or jurisdiction before officers can secure one. That practical mobility makes a warrantless vehicle search reasonable when the circumstances justify immediate action.

Early federal customs and forfeiture statutes, enacted by the same early Congresses that framed the Fourth Amendment, permitted warrantless searches of vessels and vehicles suspected of carrying unlawfully imported goods. At the same time, those statutes generally required warrants to search dwellings and similar fixed places. This longstanding distinction supported the constitutionality of treating automobiles differently from homes.

The Court also read the Prohibition Act and its supplemental legislation as preserving this distinction. Congress criminalized warrantless searches of private dwellings, but allowed officers to search other property without a warrant so long as the search was not malicious and was supported by reasonable cause. That legislative history confirmed that Congress did not intend to require a warrant before every automobile search.

The defendants argued that transporting liquor was ordinarily a misdemeanor and that, at common law, an officer could not make a warrantless arrest for a misdemeanor unless the offense occurred in the officer's presence. They maintained that the officers therefore could not search the car unless they directly sensed the liquor before stopping it.

The Court rejected that framework because Section 26 of the Prohibition Act was directed principally at stopping, seizing, and destroying illegally transported liquor. Forfeiture of the vehicle and arrest of the driver were incidental to that central purpose. The search and seizure could therefore precede the arrest rather than depend upon it.

The statutory word "discover" did not require an officer to see, smell, or otherwise directly perceive liquor in a passing automobile. It included a conclusion reasonably drawn from reliable information and known facts identifying the vehicle as one likely being used to transport contraband. The governing standard was whether the officer had reasonable or probable cause for that conclusion.

Probable cause exists when facts and circumstances known to an officer, including reasonably trustworthy information, would warrant a prudent and cautious person in believing that an offense has been committed. Good faith alone is not enough; the belief must be objectively reasonable.

The agents knew that Carroll and Kiro had participated in an attempted whisky sale, had previously driven the same automobile toward Detroit, and were later found together in that car traveling from Detroit toward Grand Rapids. Detroit was a well-known center for the illegal importation and distribution of liquor, while Grand Rapids was where the agents had reason to believe the defendants sold it.

Taken together, the defendants' suspected bootlegging activity, their use of the same car, their prior trip in the direction of Detroit, and their return from that direction supplied more than a mere hunch. The officers therefore had probable cause to stop the automobile, search it, seize the liquor, and use the liquor as evidence at trial.