D was driving a 1987 Ford Taurus station wagon. D attempted to enter the United States in southern California. A customs inspector conducted an inspection of the station wagon. D was requested to leave the vehicle. The vehicle was then taken to a secondary inspection station. It was discovered that the tank sounded solid. The gas tank was removed, and the agents found 37 kilograms of marijuana bricks. D was indicted on one count of unlawfully importing marijuana and one count of possession of marijuana with intent to distribute. D filed a motion to suppress the marijuana recovered from the gas tank. The District Court held that reasonable suspicion was required to justify the search and, accordingly, granted D's motion to suppress. The Court of Appeals affirmed. The Supreme Court granted certiorari.