In Michigan v. DeFillippo, 443 U.S. 31 (1979), the United States Supreme Court ruled that an arrest made in good faith reliance on an ordinance, which at the time had not been declared unconstitutional, is valid regardless of a subsequent judicial determination of the ordinance's unconstitutionality. The court did recognize a "possible exception" for a law "so grossly and flagrantly unconstitutional that any person of reasonable prudence would be bound to see its flaws." (Id., at p. 38.) The Court held that an arrest made in good faith reliance on an ordinance, which at the time had not been declared unconstitutional, is valid regardless of a subsequent judicial determination of its unconstitutionality. The court in DeFillippo focused upon the reasonableness of the arresting officer's conduct. It began its analysis with the fundamental principle that "the Constitution permits an officer to arrest a suspect without a warrant if there is probable cause to believe the suspect has committed or is committing an offense." (443 U.S. at p. 36.) The court then concluded that, in the case before it, there was abundant probable cause to believe that defendant's conduct violated the terms of the ordinance. It held that the subsequently determined invalidity of the ordinance did not undermine the validity of the arrest, emphasizing that probable cause is determined by looking to the "facts and circumstances within the officer's knowledge." (Id., at p. 37.) It concluded that the officer should not be required to anticipate a future holding by the courts but may reasonably rely upon the constitutional validity of the ordinance when effecting the arrest. The court stated (at p. 38): "Police are charged to enforce laws until and unless they are declared unconstitutional. The enactment of a law forecloses speculation by enforcement officers concerning its constitutionality -- with the possible exception of a law so grossly and flagrantly unconstitutional that any person of reasonable prudence would be bound to see its flaws. Society would be ill served if its police officers took it upon themselves to determine which laws are and which are not constitutionally entitled to enforcement." The United States Supreme Court held that the exclusionary rule does not apply to evidence obtained as a result of an arrest made in good faith reliance on a statute later found to be unconstitutional. The Supreme Court observed that the validity of an arrest for Fourth Amendment purposes does not depend on whether the suspect actually committed a crime, but on whether the arresting officer had probable cause to believe that the suspect had violated the law. ( DeFillippo, supra, 443 U.S. at p. 36 99 S. Ct. at p. 2631.) As framed by the court, the issue in DeFillippo was straightforward: "The . . . question . . . is whether . . . the officer lacked probable cause to believe that the conduct he observed and the words spoken constituted a violation of law simply because he should have known the ordinance was invalid and would be judicially declared unconstitutional. The answer is clearly negative." (Id. at p. 37 99 S. Ct. at p. 2632.) It was critical to the court's conclusion in DeFillippo that at the time of the arrest and search, "there was no controlling precedent that this ordinance was or was not constitutional, and hence the conduct observed violated a presumptively valid ordinance. A prudent officer, in the course of determining whether respondent had committed an offense . . . should not have been required to anticipate that a court would later hold the ordinance unconstitutional." ( Id. at pp. 37-38 99 S. Ct. at p. 2632, )