Arizona v. Evans

There is, however, the "good faith" exception to the exclusionary rule, the legality of which was affirmed in a 1984 U.S. Supreme Court decision, the United States v. Leon. It allowed for evidence to be admitted in the prosecutor's case against the respondent if it is shown that the law enforcement personnel were acting on good faith--in other words, that they had reasonable cause. With this line of reasoning, the state of Arizona argued, the evidence found against Evans should indeed be admitted into the case against him. Its attorneys asserted that the exclusionary rule applies only when the police officer knows that an arrest violates the search-and-seizure tenets of the Constitution. The state also pointed out to the Supreme Court justices that such computer errors were rare, and occurred once every few years.

Evans and his lawyers claimed the "good faith" exception did not apply, that only simple police error was behind his arrest and the subsequent discovery of contraband. Their case in this regard was strong: courts in other states (California, New York, and Maryland) had declared evidence obtained for criminal trials as the result of computer error inadmissible under the exclusionary rule. In a related case, United States v. Mackey (1975) the respondent's name was in the Federal Bureau of Investigation's National Crime Information Center database, but should not have been. It was not cleared from the records, and Mackey was arrested in Nevada on an outstanding California warrant. Law enforcement authorities found a firearm, for which Mackey did not have a permit.

The Ninth Circuit Court ruled in Mackey's favor, noting that he had been deprived of his liberty without due process of law. There were similar cases in subsequent years. "Each state addressing the issue held that a computer error was a correctable mistake by the police, and that the state should not profit from its own mistakes thereby depriving a respondent of his liberty," explained C. Maureen Stinger in the Richmond Journal of Law & Technology. Furthermore, a 1985 FBI study found that computerized criminal databases may have up to 12,000 invalid or inaccurate reports transmitted on a daily basis.