The court, on a 5-4 vote, said that deliberately questioning a suspect twice – the first time without reading the Miranda warning – is usually improper.

But the court left open the possibility that some confessions obtained after double interviews would be acceptable, providing police could prove the interrogation wasn't intended to undermine the Miranda warning.

Criminal defense attorneys and civil libertarians had complained that the strategy was being used to get around the Supreme Court's landmark 1966 Miranda v. Arizona ruling, which requires that suspects in custody be told they have the right to remain silent.

The court had considered the treatment of murder suspect Patrice Seibert. The Missouri Supreme Court ruled that the two-step interrogation process used in her case was improper – a decision upheld by the nation's highest court.

Such questioning can be successful because suspects may be more willing to talk before they're told they have a right to remain silent. And when told of their rights later, they may not realize their first confession can be used against them.

"The message for officers is you have to read rights first before questioning," said Amy Bartholow, Seibert's public defender. "Criminal defendants will have more rights in the interrogation room."

Also Monday, the court sided with police in a separate Miranda case, throwing out a decision in the case of a Colorado man who had told an officer not to bother reading him the Miranda warnings.

The two cases are the final ones in the Supreme Court's sweeping look this year at Miranda and how it is followed by U.S. law enforcement.

In January, the court ruled that police may not try to wrest confessions from criminal suspects facing formal charges without telling them they have a right to see a lawyer. Then in early June, law enforcement won a second case when the court refused to require special treatment for young people under questioning by police.

It took the Supreme Court more than six months to rule in the last two cases, an extraordinarily long time. They were argued back-to-back at the court in December.

Seibert was convicted of plotting to set a 1997 fire that killed a teenager who had been staying at the family trailer in Rolla, Mo., a rural town in the Ozarks. Police said she arranged to have her home burned to cover up the death of her 12-year-old son, who had had cerebral palsy, in order to avoid neglect allegations.

Justice David Souter, writing for himself and three other liberal justices, said that the practice is worrisome because questioning tactics are taught at national training sessions.

Justice Anthony Kennedy agreed with those four that the interrogation technique "undermines the Miranda warning and obscures its meaning."

But the court left the door open for police to be able to use some confessions obtained after double interviews. Kennedy said that police must be able to prove that the interrogation was not done "in a calculated way to undermine the Miranda warning."

In a dissent, Justice Sandra Day O'Connor said it would be tough for lower courts to determine if officers had gone too far. She was joined by Chief Justice William Rehnquist and Justices Antonin Scalia and Clarence Thomas.

"In virtually every two-state interrogation case ... courts will be forced to conduct the kind of difficult, state-of-mind inquiry that we normally take pains to avoid," she wrote.

In the second case, officers had come to Samuel Patane's house to question him about a domestic case, and they told him he had a right to remain silent, but he said he already knew his warnings. He then directed them to a gun in his bedroom and was charged with illegal possession of a firearm.

The Denver-based 10th U.S. Circuit Court of Appeals ruled that the gun could not be used as evidence against Patane because its discovery was the result of a statement made without a Miranda warning.

Thomas and two other justices said a failure to give a suspect Miranda warnings did not make such evidence inadmissible in court. O'Connor and Kennedy, while not going that far, said that the government presented a strong case for allowing evidence in the Patane case.

The cases are United States v. Patane, 02-1183, and Missouri v. Seibert, 02-1371.