Believing that respondent was impersonating a police officer, petitioner Haner, a Washington State Patrol officer, pursued and pulled over respondents vehicle. While questioning respondent at the scene, petitioner Devenpeck, Haners supervisor, discovered that respondent was taping their conversation and arrested him for violating the States Privacy Act. The state trial court subsequently dismissed the charge. Respondent then filed this suit in federal court, claiming, among other things, that his arrest violated the Fourth and Fourteenth Amendments. The District Court denied petitioners qualified immunity, and the case went to trial. The jury was instructed, inter alia, that respondent had to establish lack of probable cause to arrest, and that taping police at a traffic stop was not a crime in Washington. The jury found for petitioners. The Ninth Circuit reversed, based in part on its conclusion that petitioners could not have had probable cause to arrest. It rejected petitioners claim that there was probable cause to arrest for impersonating and for obstructing a law enforcement officer, because those offenses were not "closely related" to the offense invoked by Devenpeck at the time of arrest.

Held:

1. A warrantless arrest by a law officer is reasonable under the Fourth Amendment if, given the facts known to the officer, there is probable cause to believe that a crime has been or is being committed. The Ninth Circuits additional limitation--that the offense establishing probable cause must be "closely related" to, and based on the same conduct as, the offense the arresting officer identifies at the time of arrest--is inconsistent with this Courts precedent, which holds that an arresting officers state of mind (except for facts that he knows) is irrelevant to probable cause, see Whren v. United States, 517 U. S. 806, 812-815. The "closely related offense" rule is also condemned by its perverse consequences: it will not eliminate sham arrests but will cause officers to cease providing reasons for arrest, or to cite every class of offense for which probable cause could conceivably exist. Pp. 5-9.

2. This Court will not decide in the first instance whether petitioners lacked probable cause to arrest respondent for either obstructing or impersonating an officer because the Ninth Circuit, having found those offenses legally irrelevant, did not decide that question. Pp. 9-10.

333 F. 3d 972, reversed and remanded.

Scalia, J., delivered the opinion of the Court, in which all other Members joined, except Rehnquist, C. J., who took no part in the decision of the case.

Justice Scalia delivered the opinion of the Court.

This case presents the question whether an arrest is lawful under the Fourth Amendment when the criminal offense for which there is probable cause to arrest is not "closely related" to the offense stated by the arresting officer at the time of arrest.

A

On the night of November 22, 1997, a disabled automobile and its passengers were stranded on the shoulder of State Route 16, a divided highway, in Pierce County, Washington. Alford v. Haner, 333 F. 3d 972, 974 (CA9 2003); App. 94, 98. Respondent Jerome Alford pulled his car off the road behind the disabled vehicle, activating his "wig-wag" headlights (which flash the left and right lights alternately). As he pulled off the road, Officer Joi Haner of the Washington State Patrol, one of the two petitioners here, passed the disabled car from the opposite direction. 333 F. 3d, at 974. He turned around to check on the motorists at the first opportunity, and when he arrived, respondent, who had begun helping the motorists change a flat tire, hurri