When the U.S. Supreme Court created the Fourth Amendment exclusionary rule in Weeks v. U.S. (1914) and began applying it to the states in Mapp v. Ohio (1961), the theory was that by suppressing evidence gained by unreasonable searches and seizures, courts would deter police officers from violating the Fourth Amendment.

What the exclusionary rule has actually meant in practice is that thousands (maybe millions) of criminals have been able to stop the prosecution from using critical evidence of their guilt to hold them accountable for their crimes. In the famous words of a 1926 court decision, "The criminal goes free because the constable has blundered." (People v. Defore)

In the years since the rule was first announced, the Supreme Court has acknowledged that in some circumstances, suppression of evidence would not deter police misconduct. In such cases, the exclusionary rule is not to be invoked. Examples include good-faith mistakes in obtaining search warrants (U.S. v. Leon) and in serving them (Maryland v. Garrison; Hudson v. Michigan), enforcement of statutes later invalidated by court rulings (Michigan v. DeFillippo; Illinois v. Krull), reasonable reliance on someone's apparent authority to consent to a search (Illinois v. Rodriguez), and misidentification of a person named in an arrest warrant (Hill v. California).

Suppression is also inappropriate if the evidence was derived from an "independent source," would have been located by "inevitable discovery," or followed an intervening act that "attenuated the taint" from an earlier constitutional violation.

The Supreme Court has added one more situation to the list of exceptions to the exclusionary rule: where officers reasonably rely on information coming through "official channels" and that information turns out to be erroneous, it is not necessary to suppress resulting evidence, since there is no misconduct to deter. The court has considered mistakes originating from court personnel and from law enforcement personnel.

Arizona v. Evans

Phoenix officers stopped Isaac Evans for a traffic violation. Using their mobile computer terminal, they entered Evans' name and DOB into a database that showed an outstanding arrest warrant. When they searched his car incident to arrest, officers found drugs. Evans was subsequently prosecuted on the drug charge. But he moved to suppress the evidence, because the arrest warrant on which he was arrested had in fact been quashed before his arrest. Through clerical error, court personnel had failed to correct the database entry showing an outstanding warrant.

The trial judge ordered suppression, and the Arizona Supreme Court upheld this order on Fourth Amendment grounds. The State appealed to the U.S. Supreme Court, arguing that excluding the evidence of Evans' guilt could not deter clerical error in the judicial branch of government and that the police were not guilty of any misconduct for relying in good faith on information received through official channels.

The U.S. Supreme Court agreed and reversed the suppression order, holding that the exclusionary rule should not be applied in such circumstances. Said the court: "The exclusionary rule was historically designed as a means of deterring police misconduct, not mistakes by court employees. The threat of exclusion of evidence could not be expected to deter such individuals from failing to inform police officials that a warrant had been quashed. There is no indication that the arresting officer was not acting objectively reasonably when he relied upon the computer record. [Our precedents support] a categorical exception to the exclusionary rule for clerical errors of court employees." (Arizona v. Evans)

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Herring v. U.S.

For many years, most lower courts ruled that the Evans exception should only apply to judicial errors, but not to innocent mistakes made by other members of the law enforcement community, including outside agencies, parole and probation officers, correctional officers, and others. Many court decisions ordered evidence suppressed when official misinformation came from reliable sources outside the judicial branch.

But after the Supreme Court opinion in Hudson v. Michigan cautioned judges not to apply the exclusionary rule automatically just because an error may have occurred, the Eleventh Circuit Court of Appeals denied suppression in a case involving a police error, and the case went to the Supreme Court, which issued its ruling in 2009.

During a consensual encounter with Bennie Dean Herring, officers in Coffee County, Alabama, checked his warrant status in neighboring Dale County. An employee of the Dale County Sheriff's Department mistakenly notified officers that Herring had an active arrest warrant. Minutes later, the Dale County officials discovered that the warrant had been recalled but that the computer database inexplicably had not been updated according to standard procedure. Coffee County deputies were immediately notified; however, Herring had already been arrested and searched, revealing drugs and an illegal weapon.

Herring moved to suppress the evidence, since the official misinformation had been generated by police error, rather than judicial mistake. The federal district judge denied suppression, and the Eleventh Circuit affirmed. Herring appealed to the Supreme Court. Upholding the admission of the evidence against Herring, the Supreme Court said this:

"Suppression is not an automatic consequence of a Fourth Amendment violation. Indeed, exclusion has always been our last resort, not our first impulse. We have repeatedly rejected the argument that exclusion is a necessary consequence of a Fourth Amendment violation. Instead, we have focused on the efficacy of the rule in deterring Fourth Amendment violations in the future."

With this focus, the court held that the isolated computer error that led to Herring's arrest was not an act of misconduct or culpable negligence sufficient to invoke the exclusionary rule:

"Evidence should be suppressed only if it can be said that the law enforcement officer had knowledge, or may properly be charged with knowledge, that the search was unconstitutional under the Fourth Amendment. The exclusionary rule serves to deter deliberate, reckless, or grossly negligent conduct, or in some circumstances recurring or systemic negligence. The error in this case does not rise to that level. In such a case, the criminal should not 'go free because the constable has blundered'."

The court cautioned that exclusion might still be appropriate if an error arose because a law enforcement database was poorly maintained or contained deliberate misinformation "to lay the groundwork for future false arrests." (Herring v. U.S.)

The Evans-Herring Rule

Under the combined holdings of Evans and Herring, you may reasonably rely on information coming through "official channels" to justify a detention, arrest, or search. Unless a criminal defendant can show that the source of the information is an unreliable system marked by frequent errors or containing knowingly false entries, the fact that the information you received in an isolated case turns out to have been erroneous will not trigger application of the federal exclusionary rule.

Independent State Grounds

Whenever the U.S. Supreme Court issues a new decision holding that suppression of evidence is not appropriate under the Weeks-Mapp exclusionary rule (which is followed by all federal courts and the courts of most states), it's always necessary to note that a few states base greater exclusion on their state constitutions. The highest courts of those states may issue rulings that compel wider suppression of evidence in state courts. Always check with local advisers to verify the situation in your jurisdiction.

Devallis Rutledge is a former police officer and veteran prosecutor who currently serves as Special Counsel to the Los Angeles County District Attorney. He is the author of 11 books, including "Courtroom Survival, The Officer's Guide to Better Testimony."