Over the past several decades, the Supreme Court has narrowed the scope of the exclusionary rule in Fourth Amendment cases—that is, in cases involving illegal searches or seizures. Overview of the Fourth Amendment and the Exclusionary Rule

The Fourth Amendment to the U.S. Constitution provides a right "of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures." For example, under the general rule, a police officer may not arrest a person unless a judicial magistrate has issued a warrant, based on evidence establishing sufficient probable cause, for that person's arrest. In the Fourth Amendment context, the exclusionary rule requires a trial court to forbid the prosecution's use of evidence obtained as a result of an unconstitutional search or seizure. In other cases, the Court has characterized the rule as a "judicially created remedy ... rather than a personal constitutional right." In Leon , the Court held that the exclusionary rule does not apply when police officers act with "objectively reasonable reliance" on a search warrant later found to be invalid. On appeal, the Supreme Court declined to apply the good-faith exception to the exclusionary rule, because it found that the officers' search pursuant to a warrant that failed to list property to be searched was not a "reasonable" mistake. Because the Court limited its opinion in Hudson to knock and announce violations, it was unclear after that case whether the Court would extend the good-faith exception to more serious police errors, such as those involving warrants or warrant exceptions. Herring v. United States

In Herring v. United States , a 2009 case, the Supreme Court for the first time applied the good-faith exception in a case involving police error regarding a warrant. The disagreement in the case centered on whether the exclusionary rule should apply to suppress the evidence obtained as a result of the violation. Quoting Hudson v. Michigan , the Court emphasized that the exclusionary rule is a "'last resort'" rather than a "necessary consequence of a Fourth Amendment violation." In addition to broadening the good-faith exception, the Herring decision appears to further the trend toward interpreting the exclusionary rule as lacking constitutional status.
The Fourth Amendment to the U.S. Constitution provides a right against "unreasonable searches and seizures." To deter the federal and state governments from violating this right, courts have developed an "exclusionary rule," which requires that evidence obtained as a result of an invalid search or seizure be excluded from use at trial.
The Supreme Court has narrowed the scope of the exclusionary rule in several cases since the late 1970s. In United States v. Leon, the Court created the "good-faith" exception to the exclusionary rule. The good-faith exception applies when officers conduct a search or seizure with "objectively reasonable reliance" on, for example, a warrant that is not obviously invalid but that a judicial magistrate should not have signed.
Until a 2006 case, Hudson v. Michigan, the Supreme Court had applied the good-faith exception only in cases in which the error creating the constitutional violation was caused by judicial or legislative actors, rather than by the police themselves. In Hudson, the Court applied the exception to a case in which police officers had violated the "knock and announce" rule by entering a home without waiting a sufficient period of time.
In Herring v. United States, a 2009 decision, the Supreme Court for the first time applied the good-faith exception to bar application of the exclusionary rule in a case involving police error regarding a warrant. A police officer in the case mistakenly identified an arrest warrant for the defendant. The Court held that evidence discovered after the subsequent arrest was admissible at trial because the officer's error was not "deliberate" and the officers involved were not "culpable."
In future cases, courts will apply the Herring "deliberate and culpable" test to determine whether to admit evidence obtained as a result of a search or seizure which is unconstitutional as a consequence of police error. A second impact of the Herring decision is a weaker constitutional footing for the exclusionary rule. Whereas judicially-created remedies have gained "constitutional status" in the context of some other constitutional rights, it appears that the exclusionary rule lacks such a grounding under the Court's current Fourth Amendment jurisprudence.