In Herring v United States  USSC 14 January 2009 the majority (5-4) held that the basis for exclusion of evidence obtained in breach of the Fourth Amendment (the right not to be subjected to unreasonable search or seizure) is deterrence of official misconduct.
Prior to that decision reasons other than deterrence could have been advanced for exclusion of wrongfully obtained evidence. These were mentioned in the leading dissenting opinion of Ginsburg J: the need to constrain state power, to avoid taint to the judiciary from a perception of partnership in official lawlessness, to avoid undermining popular trust in government, to withhold constitutional approval of misconduct, to maintain respect for the law, and to provide the only practical remedy for official impropriety.
But no, held Roberts CJ, joined by Scalia, Kennedy, Thomas and Alito JJ. If deterrence would not be effective there is no point in excluding evidence: the benefits of deterrence must outweigh the costs of excluding the evidence. These costs are the price paid by the justice system in allowing the particular offender to go free:
"To trigger the exclusionary rule, police conduct must be sufficiently deliberate that exclusion can meaningfully deter it, and sufficiently culpable that such deterrence is worth the price paid by the justice system. As laid out in our cases, the exclusionary rule serves to deter deliberate, reckless, or grossly negligent conduct, or in some circumstances recurring or systemic negligence."
In Herring the police mistakenly believed that there was in existence a warrant to arrest Mr Herring. That belief arose from a check on the database maintained by the local police. Before a copy of the warrant could be faxed to them, officers arrested and searched Mr Herring, finding drugs and a gun he was not entitled to possess. Within a few minutes the staff at the station realised that, as they could not locate the paper copy of the warrant their database must have been in error, so the arresting officers were informed. The evidence had already been discovered.
Was this a slight error arising from the system in place at the relevant station not being operated efficiently? The majority held that it was. There was no flagrant and deliberate disregard of Mr Herring's constitutional rights that would have been necessary to trigger the need for the deterrent response of exclusion of the evidence.
The minority strongly dissented on this point. Ginsburg J emphasised the need for computerised systems to be efficiently maintained in order to protect innocent people from this sort of conduct:
"Inaccuracies in expansive, interconnected collections of electronic information raise grave concerns for individual liberty. "The offense to the dignity of the citizen who is arrested, handcuffed, and searched on a public street simply because some bureaucrat has failed to maintain an accurate computer data base" is evocative of the use of general warrants that so outraged the authors of our Bill of Rights. Evans, 514 U. S., at 23 (STEVENS, J., dissenting)."
She disagreed with the majority argument that deterrence would not be effective against conduct that is merely negligent, pointing out that the law of torts is based on the assumption that liability for negligence will make people more careful.
There was no evidence that in this case the systemic errors were ingrained and frequent, and Roberts CJ regarded it as significant that they were not routine or widespread. If they were, deterrence would have been necessary on the basis that the misconduct had graduated from negligence to recklessness:
"If the police have been shown to be reckless in maintaining a warrant system, or to have knowingly made false entries to lay the groundwork for future false arrests, exclusion would certainly be justified under our cases should such misconduct cause a Fourth Amendment violation."
So, apparently widespread negligence would not call for deterrence unless it could be reclassified as recklessness.
In computerised databases errors can easily become widespread. False information about one person can become available to a large number of officials. There are good policy reasons for imposing on such a potentially error-prone system the safeguard of deterrence of negligent administration. Certainly it is appropriate to assess the circumstances of each case and to weigh the seriousness of the official misconduct against the public interest in admitting the wrongfully obtained evidence, but it seems to be wrong to impose a rule that negligent errors do not count as official misconduct.
Herring marks a significant departure from the Katz v United States, 389 U.S. 347 (1967) focus on privacy interests. Like anyone who did not have a warrant out for his arrest, Mr Herring had, one would have thought on the basis of Katz, a reasonable expectation of privacy in relation to his person and his vehicle, at the time of his wrongful arrest. It was insufficient to justify the unauthorised interceptions in Katz that the Government’s agents acted in good faith and circumscribed their activities to the minimum they considered necessary, and the interceptions where held to amount to a bypassing of a neutral predetermination of the scope of the search which left the police to determine the scope of the Fourth Amendment protection. So too in Herring, the absence of a warrant to arrest him meant that the police, albeit innocently, determined – and terminated – his constitutional protection. Acting in good faith can hardly be a reason to admit wrongfully obtained evidence, because the police are expected always to act in good faith. Katz was not referred to in Herring. The breach of the privacy right in Herring was serious. That is not to say that the Court was wrong to rule the evidence admissible, because the balancing of this breach (measured as a breach of privacy) against the cost to the enforcement of the law might still have supported that result. The focus on the police misconduct was a very small part of the whole picture.