Arizona v. Johnson
In Arizona v. Johnson, U.S. 129 S.Ct. 781, 784,172 L. Ed. 2d 694 (2009), the passenger of a car that had been validly stopped for a traffic violation agreed to answer questions about an unrelated matter while the driver's documents were being cleared. Id. at 784-85.
Prior to beginning the questioning, the passenger was subjected to an involuntary pat-down; a gun was found, and the passenger was arrested as a prohibited possessor. Id. at 785.
Upon review, the United States Supreme Court held that the pat-down was not a violation of the passenger's Fourth Amendment rights because it was conducted during a valid stop that had not yet evolved into a consensual encounter; a distinction the Court found to be noteworthy. Id. at 787-88.
In Arizona v. Johnson, the United States Supreme Court held "in a traffic-stop setting, the first Terry condition--a lawful investigatory stop--is met whenever it is lawful for police to detain an automobile and its occupants . . . the police need not have, in addition, cause to believe any occupant of the vehicle is involved in criminal activity." Id. at 327.
However, to justify a frisk of a passenger during a traffic stop, "just as in the case of a pedestrian reasonably suspected of criminal activity, the police must harbor reasonable suspicion that the person subjected to the frisk is armed and dangerous." Id.