Maryland v. Garrison

The exclusionary rule was developed to enforce Fourth Amendment search and seizure requirements in its exclusion from the criminal courtroom of evidence obtained by other than legal means. The good faith exception to the exclusionary rule, on the other hand, offers law-enforcement officers an area of leeway--opponents would call it a loophole--within the legal confines of the exclusionary rule. Thus when a search turns out to be illegal, but while conducting it the police officers believed in good faith that they were operating within the law, the evidence obtained in such a search is deemed admissible.

Such was the situation in United States v. Leon (1984), in which Justice Byron White articulated the good faith exception as a modification of the exclusionary rule to uphold the admissibility of "evidence seized on a search warrant issued by a detached and neutral magistrate but ultimately found to be unsupported by probable cause."

Views on the good faith exception that, like the exclusionary rule, applies to criminal proceedings, vary depending on whether the commentator is a civil libertarian or someone whose primary emphasis is on law and order.