The United States Supreme Court today ruled that jurors may hear evidence discovered in a search based on faulty information in a police computer database.

The court ruled that the US constitution's protections against unreasonable search and seizure do not exclude evidence gained through "isolated negligence" where there is no evidence of police wrongdoing.

In a 5-4 decision, the high court found that if police wrongly believe they have an arrest warrant because a computer database contains an incorrect entry indicated the existence of a warrant, evidence they discover upon making the arrest may be used to prosecute the defendant.

The decision could have far-reaching consequences, as law enforcement use of electronic databases grows.

In the case in question, a Alabama man, Bennie Dean Herring, was arrested when a police computer showed he was wanted on an arrest warrant in a neighbouring county. An investigator then searched his truck and found methamphetamine and an illegal pistol. When officers sought to retrieve the initial arrest warrant just minutes later, they discovered it had been cancelled five months earlier, though the entry had not been removed from the police computer.

In a federal court hearing soon after the arrest, Herring asked the judge to suppress the gun and the methamphetamine, arguing the search was illegal because the arrest warrant had been rescinded and police had no other justification for a search.

A judge denied Herring's motion, saying that exclusion of the evidence would do little to deter similar police errors in the future, and an appeals court later agreed.

Writing for the majority, Chief Justice John Roberts, a Bush appointee and conservative voice on the court, found that the mere fact of an illegal search does not necessitate throwing out the evidence obtained. He wrote that if evidence is to be excluded, the exclusion must effectively deter future illegal searches.

"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," he wrote. But in Herring's case, the police error was isolated, so the gun and drugs may be used in court.

Roberts was joined in the opinion by the court's conservative bloc - Antonin Scalia, Clarence Thomas and Samuel Alito - and by Anthony Kennedy, considered a swing vote.

Dissenting were the court's liberal bloc, Ruth Bader Ginsburg, John Paul Stevens, David Souter and Steven Breyer.

In the dissenting opinion, Ginsburg wrote that exclusion of evidence is a defendant's "redress" for an illegal search.

"The court's opinion underestimates the need for a forceful exclusionary rule and the gravity of record-keeping errors in law enforcement," she wrote.

Ginsburg also disagreed with the majority's assertion that the exclusion of evidence in this type of case would be unlikely to deter future police negligence. She wrote that the Dale County, Alabama, sheriff's department, which made the mistake, could have a established a routine practice of checking the computer database for accuracy, and noted that the scope and influence of law enforcement databases has expanded dramatically in recent years.

"By restricting suppression to bookkeeping errors that are deliberate or reckless, the majority leaves Herring, and others like him, with no remedy for violations of their constitutional rights," she wrote.

The case is a timely reminder of one of the key tasks facing Barack Obama in his coming White House term. In recent years, the supreme court has decided some of the most ideologically charged cases by a 5-4 decision, with the nine justices split into reliable voting blocs.

As many as three US supreme court justices are likely to retire in the next four years, giving Obama an opportunity to nominate justices that share his views on abortion, constitutional rights of terrorism suspects and criminal defendants, separation of church and state, and other contentious social and legal issues. The nine high court justices hold lifetime appointments and must be confirmed by the Senate.