Temporary detention of individuals during the stop of an automobile by the police, even if only for a brief period and for a limited purpose, constitutes a "seizure" of "persons" within the meaning of U.S. Const. amend. IV. An automobile stop is thus subject to the constitutional imperative that it not be "unreasonable" under the circumstances. As a general matter, the decision to stop an automobile is reasonable where the police have probable cause to believe that a traffic violation has occurred.
Whren and Brown were indicted on federal drug charges when drug evidence was seized after their truck was stopped, on the asserted ground of observed traffic violations, by District of Columbia plainclothes vice squad police officers who were patrolling in an unmarked car in a "high drug area." At a pretrial suppression hearing in the district court, Whren and Brown argued that the stop was not justified by probable cause, or even reasonable suspicion, to believe that the accused had been engaged in illegal drug dealing, and the asserted traffic-violation motive for the stop was pretextual. The district court denied the accuseds' motion to suppress the drug evidence, finding that the officers had probable cause to believe that the traffic code was violated and that there was nothing to demonstrate that the officers' actions were contrary to a normal traffic stop. Whren and Brown were then convicted on the pertinent drug charges. The court of appeals affirmed the view that with respect to the suppression issue, a traffic stop was permissible -- regardless of whether a police officer subjectively believed that the occupants of an automobile might be engaging in some other illegal behavior -- as long as a reasonable officer in the same circumstances "could have" stopped the car for the suspected traffic violation.
Did the officers have probable cause to believe defendants violated the traffic code, thus, rendering the vehicle stop reasonable and the evidence seized admissible?
It was held that the Supreme Court would not replace the normal test under the Federal Constitution's Fourth Amendment, which was that the decision to stop an automobile is reasonable if the police have probable cause to believe that a traffic violation has occurred. The Court rejected the alternative standard suggested by defendants, which would depend on whether a police officer, acting reasonably, would have made the automobile stop for the reason given. Thus, the District Court's probable-cause finding, which Whren and Brown accepted, rendered the stop of the their truck reasonable under the Fourth Amendment, the evidence thereby discovered was admissible, and the Court of Appeals' upholding of the Whren and Brown's convictions was correct.