Last September 11, after the 19 hijackers had completed their ghastly work, the government had in its custody a man suspected by FBI agents of being part of the plot-a man they thought might have information about other co-conspirators or planned attacks. He had been locked up since mid-August, technically for overstaying his visa, based on a tip about his strange behavior at a Minnesota flight school. Even before September 11, agents had strongly suspected that he was a dangerous Islamic militant plotting airline terrorism.

But the FBI did not interrogate Zacarias Moussaoui, who is now alleged to be the "20th hijacker" and who has admitted membership in Al Qaeda. "We were prevented from even attempting to question Moussaoui on the day of the attacks when, in theory, he could have possessed further information about other co-conspirators," complained Coleen Rowley, a lawyer in the FBI’s Minneapolis office, in a little-noticed portion of her much-publicized May 21 letter to FBI Director Robert S. Mueller III.

The reason for this reticence was that Moussaoui had requested a lawyer. To the FBI that meant that any further interrogation would violate the Fifth Amendment rules laid down by the Supreme Court, in cases including Miranda v. Arizona in 1966.

It’s not hard to imagine such rules leading to the loss of countless lives. While interrogating Moussaoui on September 11 might not have yielded any useful information, suppose that he had been part of a team planning a second wave of hijackings later in September and that his resistance could have been cracked. Or suppose that the FBI learns tomorrow, from a wiretap, that another Al Qaeda team is planning a big terrorist attack sometime in August and arrests an occupant of the wiretapped apartment.

We all know the drill: Before asking any questions, FBI agents (and police) must give the suspect the Miranda warnings: "You have a right to remain silent," and so forth. And if the suspect asks for a lawyer, all interrogation must cease until the lawyer arrives (and tells the suspect to keep quiet). This seems perverse when dealing with people suspected of planning mass murder. But it’s the law, isn’t it?

Actually, it’s not the law, even though many judges think it is, along with most lawyers, federal agents, police, and cop-show mavens. To the contrary (in my view), the law allows agents and police to interrogate any suspect without Miranda warnings; to tell the suspect he does not have a right to remain silent; to spurn any request for a lawyer-and in a terrorism investigation, perhaps even to use hours of interrogation, verbal abuse, isolation, blindfolds, polygraph tests, death-penalty threats, and other forms of psychological coercion short of torture or physical brutality.

That’s my opinion, at least, and I’m sticking to it unless and until the Supreme Court says I’m wrong. While this view appears to contradict the language of some precedents, including Miranda, I’m hoping that the justices will confirm it in a case to be heard this fall, Chavez v. Martinez.

The explanation for my apparent heresy is that the Fifth Amendment’s self-incrimination clause says only that no person "shall be compelled in any criminal case to be a witness against himself." This prohibits forcing a defendant to testify at his trial and also making him a witness against himself indirectly by using compelled pretrial statements. It does not prohibit compelling a suspect to talk.

Nor does Miranda, which held only that in determining whether a defendant’s statements (and information derived from them) may be used against him at his trial, courts must treat all interrogations of arrested suspects as inherently coercive unless the warnings were given.

Courts typically ignore this distinction because in almost every litigated case, the issue is whether a criminal defendant’s incriminating statements should be suppressed at trial; there is no need to focus on whether the constitutional problem is the conduct of the interrogation itself, or the use at trial of evidence obtained, or both. And as a matter of verbal shorthand, it’s a lot easier to say, "The police violated Miranda" than to say, "The judge would be violating Miranda if he or she were to admit the defendant’s statements into evidence at his trial."

But the war against terrorism has suddenly increased the importance of this previously academic question. In terrorism investigations, it will often be more important to get potentially life-saving information from a suspect than to obtain incriminating statements for use in court.

And the justices could provide valuable guidance when they decide Chavez v. Martinez. In what lower courts found to be a coercive interrogation, a police officer named Ben Chavez insistently questioned one Oliverio Martinez, without any Miranda warnings, as he struggled for his life in a hospital, suffering from several police-inflicted gunshot wounds. Martinez later brought a civil suit against the police, including Chavez. One argument for dismissing the claim against Chavez was that he had done nothing illegal because the self-incrimination clause could be violated only by the use of evidence at a criminal trial. But a federal appeals court (the 9th Circuit) ruled that "Chavez’s coercive questioning violated Martinez’s … rights" under the self-incrimination clause.

Some Supreme Court precedents suggest the contrary. In 1990, in United States v. Verdugo-Urquidez, the Court said that "a constitutional violation [of the self-incrimination clause] occurs only at trial." It cited an earlier ruling that the government can compel reluctant witnesses to talk if it first guarantees them immunity from prosecution on the basis of their statements or of any evidence derived from their statements.

All of this suggests that the self-incrimination clause "does not forbid the forcible extraction of information but only the use of information so extracted as evidence in a criminal case," as another federal appeals court (the 7th Circuit) ruled in 1992, in Mahoney v. Kesery.

Of course, even when the primary reason for questioning a suspected terrorist is prevention, the government could pay a heavy cost for ignoring Miranda and using coercive interrogation techniques: It could sometimes make it difficult or impossible to prosecute extremely dangerous terrorists.

But terrorism investigators may be able to get their evidence and use it too-if the Court (or Congress) extends a 1984 precedent, New York v. Quarles. In arresting a man with an empty shoulder holster who had been seen entering a grocery store carrying a gun, a policeman demanded to know where the gun was. The suspect pointed to where it was hidden. The justices upheld the use of this incriminating answer at his trial, stating that in such unusual circumstances, "There is a `public safety’ exception" to Miranda.

Quarles is not a perfect template for most terrorism investigations because of the immediate nature of the danger in that case (an accomplice or someone else might have picked up the gun) and the spontaneity of the officer’s question. But when the main purpose of the interrogation is to prevent terrorist attacks, the magnitude of the danger argues for a broader public safety exception.

Would investigators routinely ignore Miranda and engage in coercive interrogation if they were told that doing so would be constitutional? The risk seems modest. Police would still need to comply with Miranda in almost all cases for fear of jeopardizing any prosecution. While that would not be true in terrorism investigations (if Quarles is read broadly), extreme abuses such as beatings and torture would violate another clause of the Fifth Amendment (and of the 14th Amendment as well). That is the due process clause, which has long been construed as barring extreme abuse of suspects.

Should even torture be allowed in rare cases in which many lives could be saved, as Harvard Law School’s Alan Dershowitz and others argue? Surely, they say, torturing a captured terrorist would be morally and legally justified if that were the only hope of finding a ticking nuclear time bomb that could kill 100,000 people.

But because such a case is extremely unlikely ever to occur in the real world, it would be a mistake to enshrine in the law an exception to the absolute rule against torture. It is almost always impossible to be confident in advance that a suspect has potentially life-saving information. And no "torture exception" could be defined narrowly enough to prevent overuse. Would we want our government torturing suspects like Moussaoui because they might possibly know something about planned attacks? If the hope of saving 100,000 lives justifies torture, what about 1,000? Or 100? Or 10? Or one?

That slope is too slippery. And if anything like the ticking-nuclear-time-bomb hypothetical ever does occur, no jury in the world would convict investigators for doing what they had to do.