Respondent was arrested by Phoenix police during a routine traffic stop when a patrol cars computer indicated that there was an outstanding misdemeanor warrant for his arrest. A subsequent search of his car revealed a bag of marijuana, and he was charged with possession. Respondent moved to suppress the marijuana as the fruit of an unlawful arrest, since the misdemeanor warrant had been quashed before his arrest. The trial court granted the motion, but the Court of Appeals reversed on the ground that the exclusionary rules purpose would not be served by excluding evidence obtained because of an error by employees not directly associated with the arresting officers or their police department. In reversing, the Arizona Supreme Court rejected the distinction between clerical errors committed by law enforcement personnel and similar mistakes by court employees and predicted that the exclusionary rules application would serve to improve the efficiency of criminal justice system recordkeepers.

Held:

1. This Court had jurisdiction to review the State Supreme Courts decision. Under Michigan v. Long, 463 U.S. 1032, when a state-court decision fairly appears to rest primarily on federal law, or to be interwoven with federal law, and when the adequacy and independence of any possible state-law ground is not clear from the opinions face, this Court will accept as the most reasonable explanation that the state court decided the case the way it did because it believed that federal law required it to do so. This standard for determining whether a state-court decision rests upon an adequate and independent state ground was adopted (1) to obviate the unsatisfactory and intrusive practice of requiring state courts to clarify their decisions to this Courts satisfaction and (2) to provide state Page II judges with a clearer opportunity to develop state jurisprudence unimpeded by federal interference and yet preserve the federal laws integrity. Michigan properly serves it purpose and should not be disturbed. State courts are free both to interpret state constitutional provisions to accord greater protection to individual rights than do similar provisions of the United States Constitution and to serve as experimental laboratories. However, in cases where they interpret the United States Constitution, they are not free from the final authority of this Court. In this case, the State Supreme Court based its decision squarely upon its interpretation of federal law when it discussed the appropriateness of applying the exclusionary rule, and it offered no plain statement that its references to federal law were being used only for the purpose of guidance and did not compel the result reached. Pp. 4-7.

2. The exclusionary rule does not require suppression of evidence seized in violation of the Fourth Amendment where the erroneous information resulted from clerical errors of court employees. The exclusionary rule is a judicially created remedy designed to safeguard against future violations of Fourth Amendment rights through its deterrent effect. However, the issue of exclusion is separate from whether the Amendment has been violated. The Amendment does not expressly preclude the use of evidence obtained in violation of its commands, and exclusion is appropriate only where the rules remedial objectives are thought most efficaciously served. The same framework that this Court used in United States v. Leon, 468 U.S. 897, to determine that there was no sound reason to apply the exclusionary rule as a means of deterring misconduct on the part of judicial officers responsible for issuing search warrants applies in this case. The exclusionary rule was historically designed as a means of deterring police misconduct, not mistakes by court employees. See id., at 916. In addition, respondent offers no evidence that court employees are inc