The Martinez case examined whether the Constitution protects a person when he is being questioned by police, or only later at a future trial.
In past decades, the more liberal Supreme Court had said that suspects and witnesses had a right to remain silent. The 1966 decision in Miranda vs. Arizona held that police officers must tell people of their rights before questioning them.
Similarly, unwilling witnesses called before investigating committees had the right to "plead the 5th Amendment" and thereafter refuse to testify.
But in Tuesday's opinion, the court majority said that the 5th Amendment comes into play only later, when a suspect is tried in court.
Despite a common perception, the Constitution does not bar police from using pressure -- short of torture -- to obtain information from suspects or witnesses, said Justice Clarence Thomas in the court's lead opinion.
"Mere compulsive questioning [does not] violate the Constitution," Thomas said. He dismissed the view adopted by federal judges in California that "coercive police interrogations, absent the use of the involuntary statements in a criminal case, violates the 5th Amendment's Self-Incrimination Clause."
Chief Justice William H. Rehnquist and Justices Antonin Scalia and Sandra Day O'Connor agreed with Thomas.
Justices David H. Souter and Stephen G. Breyer concurred on the issue of barring the use of compelled confessions in court. However, in a separate opinion, they said "outrageous conduct by the police" still might violate a witness' constitutional right to "due process of law."
Three justices who sided with the Oxnard farm worker -- Justices John Paul Stevens, Ruth Bader Ginsburg and Anthony M. Kennedy -- agreed with Souter and Breyer that police can be sued for "outrageous conduct" during an investigation.
In a long dissent, Kennedy said the court was abandoning a historic understanding of the 5th Amendment.
"This is no small matter. To tell our whole legal system that, when conducting a criminal investigation, police officers can use severe compulsion, even torture, with no present violation of the right against compelled self-incrimination can only diminish a celebrated provision in the Bill of Rights," Kennedy wrote. "A Constitution survives over time because the people share a common, historic commitment to certain simple but fundamental principles which preserve their freedom. Today's decision undermines one of those respected precepts."
