A disabled automobile and its passengers were stranded on the shoulder of State Route 16. Alford (P) pulled his car off the road behind the disabled vehicle, activating his 'wig-wag' headlights (which flash the left and right lights alternately). Haner (D) of the Washington State Patrol passed the disabled car from the opposite direction. He turned around to check on the motorists at the first opportunity, and when he arrived, P, who had begun helping the motorists change a flat tire, hurried back to his car and drove away. The stranded motorists asked D if P was a 'cop'; they said that respondent's statements, and his flashing, wig-wag headlights, had given them that impression. D radioed his supervisor, Sergeant Gerald Devenpeck (D1) that he was concerned respondent was an 'impersonator' or 'wannabe cop.' P's car was pulled over. D observed P was listening to the Kitsap County Sheriff's Office police frequency on a special radio, and that handcuffs and a hand-held police scanner were in the car. P seemed untruthful and evasive. D1arrived on the scene a short time later. In the course of his questioning, D1 noticed a tape recorder on the passenger seat with the play and record buttons depressed. D1 discovered that P had been recording his conversations with the officers. P was arrested for a violation of the Washington Privacy Act, Wash. Rev. Code §9.73.030 (1994). 333 F. 3d, at 975; App. 144-145. P claimed that a state court-of-appeals decision, a copy of which he claimed was in his glove compartment, permitted him to record roadside conversations with police officers. D1 returned to his car, reviewed the language of the Privacy Act, and attempted unsuccessfully to reach a prosecutor to confirm that the arrest was lawful. P was taken to jail. D1 and a deputy county prosecutor discussed a series of possible criminal offenses, including violation of the Privacy Act, impersonating a police officer, and making a false representation to an officer. It was suggested that P be charged with 'obstructing a public servant' 'based on the runaround [he] gave [Devenpeck].' D1 rejected this suggestion, explaining that the State Patrol does not, as a matter of policy, 'stack charges' against an arrestee. D charged P with violating the State Privacy Act and issued a ticket to P for his flashing headlights under Wash. Rev. Code §46.37.280(3) (1994), App. 24-25. The state trial court subsequently dismissed both charges. P filed suit against Ds in Federal District Court. He asserted a federal cause of action under Rev. Stat. §1979, 42 U. S. C. §1983, and a state cause of action for unlawful arrest and imprisonment, both claims resting upon the allegation that Ds arrested him without probable cause in violation of the Fourth and Fourteenth Amendments. The District Court denied Ds' motion for summary judgment on grounds of qualified immunity, and the case proceeded to trial. The jury was instructed that P's taping of petitioners was not a crime. The jury was directed that it must find for Ds if a reasonable officer in the same circumstances would have believed P's detention was lawful. The jury returned a unanimous verdict in favor of Ds. The District Court denied P's motion for judgment as a matter of law or, in the alternative, a new trial, and P appealed. A divided panel of the Court of Appeals for the Ninth Circuit reversed, finding 'no evidence to support the jury's verdict.' The majority concluded that petitioners could not have had probable cause to arrest because they cited only the Privacy Act charge and 'tape recording officers conducting a traffic stop is not a crime in Washington.' The majority rejected petitioners' claim that probable cause existed to arrest respondent for the offenses of impersonating a law-enforcement officer and obstructing a law-enforcement officer, because, it said, those offenses were not 'closely related' to the offense invoked by D1 as he took respondent into custody. The majority also held that there was no evidence to support Ds' claim of qualified immunity.