At his trial for unlawful possession of a weapon, William Wardlow argued that the police did not have grounds to stop him. The trial court rejected this argument and he was convicted. The Illinois Supreme Court reversed the conviction. The United States Supreme Court accepted the case for review.

The Court's Decision

In a 5-4 decision, the Court held that police may consider a suspect's unprovoked flight as one factor contributing to “reasonable suspicion“ justifying an investigatory stop. Chief Justice Rehnquist wrote for the majority. In Terry v. Ohio, 1968, the Court had ruled that the Fourth Amendment permits an officer to conduct a brief investigatory stop when there is reasonable suspicion of criminal activity. In Illinois, the Court relied on that ruling, as well as on precedents from other cases in which presence in a high crime area and unprovoked flight could be used by the police as factors contributing to “reasonable suspicion.“

Justice John Paul Stevens wrote an opinion concurring in part and dissenting in part. He agreed with the Chief Justice that flight will not always justify stopping a suspect. There could be many innocent explanations: “A pedestrian may break into a run for a variety of reasonsâ¦any of which might coincide with the arrival of an officer in the vicinity.“ Some innocent people may nonetheless wish to avoid contact with the police. “Among some citizens, particularly minorities and those residing in high crime areas, there is also the possibility that the fleeing person is entirely innocent, but, with or without justification, believes that contact with the police can itself be dangerousâ¦.“

Justice Stevens noted that there was no testimony that the police cars were marked, that the other officers were in uniform, or that Wardlow realized they were police. There was no reasonable suspicion to stop him, and the fact that he chose to run does not provide the missing evidence.