It would be no loss to humanity if we dragged Zacarias Moussaoui in front of a firing squad tomorrow and shot him. He has boasted in open court of being a "member of Al Qaeda" and loyal to Osama bin Laden, and of knowing "exactly who" committed the 9/11 mass murders. He has declared, "I, Zacarias Moussaoui, urge, incite, encourage, solicit Muslim to kill Americans, civilian or military, anywhere around the world." He is crazy and evil.

But Attorney General John Ashcroft seems so eager to kill the man that he would shoot a hole in the Constitution to get him. Ashcroft wants to put Moussaoui on trial for the capital crime of complicity in the 9/11 plot, without letting his lawyers take the testimony of three captured Qaeda leaders who may have told interrogators that Moussaoui did not participate in it. That’s the watered-down notion of justice that an Ashcroft subordinate urged a federal appeals court in Richmond, Va., to endorse on December 3.

The appeals court should say no. This might keep Ashcroft from getting the death sentence he craves for Moussaoui, since the charges connecting Moussaoui to 9/11 — which Moussaoui denies, and for which the evidence seems thin — appear to be the only ones punishable by death under current law. But Moussaoui is doomed to die in prison in any event, of old age if not by execution. And the difference between killing him and locking him up forever is simply not important enough to justify an unfair trial. Indeed, putting Moussaoui to death would be so idiotic that it’s hard to believe any sensible official really wants to do it: He’s nuttier than a fruitcake, his French mother is an articulate and sympathetic advocate for mercy, and he would be featured as a martyr on Qaeda recruiting posters all over the world. Killing Moussaoui would only increase the supply of terrorists bent on killing Americans.

The government claims that allowing Moussaoui’s lawyers to question captured Qaeda leaders would disrupt interrogations that could be vital to protecting national security and American lives. U.S. District Judge Leonie Brinkema, of Alexandria, Va., rightly deferred to that claim. But she was also right to rule, in a series of decisions between January and October, that the government cannot prosecute Moussaoui or seek the death penalty on the 9/11-related charges while denying the defense access to witnesses who "could offer testimony which would undermine" those charges. (Brinkema’s related decision to exclude from any Moussaoui trial emotionally packed evidence of the 9/11 massacres, such as cockpit voice recordings and video of the World Trade towers falling, is far more questionable.)

Brinkema based her finding that the testimony would be exculpatory — which the government disputes — on classified summaries of interrogations of the captured Qaeda leaders. One of them is Ramzi Binalshibh, who helped plan the attacks and sent Moussaoui money. Binalshibh has reportedly told interrogators that Moussaoui was sent to America for a planned post-9/11 attack, as Moussaoui himself has said. While no Qaeda member is credible, lack of credibility is no basis for denying a defendant the right to call witnesses who have relevant information. Brinkema struck the right balance by barring pursuit of either the 9/11-related charges or the death penalty as long as the government refuses to allow depositions of the Qaeda witnesses to be taken by remote video hookup from the secret locations overseas where they are being held.

The Moussaoui case has been widely described as presenting a fundamental clash between national security and fair-trial rights. But the clash can be avoided. The government will still retain three options for keeping Moussaoui locked up without producing the witnesses, even if the court rejects Ashcroft’s appeal of Brinkema’s ruling. The first option is to proceed to trial before Brinkema on the remaining charges in the indictment, which are based on Moussaoui’s admitted role in the global Qaeda conspiracy to murder Americans; those charges can bring life in prison, and Brinkema held that they could fairly be tried without the testimony of the captured Qaeda leaders. The second and perhaps likeliest option is to try Moussaoui before a special military commission. The third option is to detain him without trial, as an unlawful enemy combatant, until we have wiped out Al Qaeda and thus won the war it launched.

I have condemned the Bush administration’s denial of any semblance of due process to the three men in military brigs in the United States and the more than 600 at Guantanamo whom it has detained without trial as enemy combatants. The Supreme Court should reject this claim to be above the law. But I don’t dispute the government’s power to detain proven enemy combatants until they are no longer dangerous. While a hearing before some kind of tribunal should be required to establish enemy-combatant status, the process could be far less elaborate and the burden of proof lighter than it is at a criminal trial.

Indeed, the Moussaoui case demonstrates that preventive detention (or military trial) of enemy combatants — whether by military or civilian authorities — may in some cases be a necessary, as well as a sufficient, alternative to ordinary criminal prosecution. It may be necessary because, as the government points out, Brinkema’s ruling would force dismissal of all criminal charges against an accused terrorist in any case in which all charges are disputed by captured confederates whom the government bars from testifying. There may not be many such cases, but there could be some. Those civil libertarians who would rule out both preventive detention and military trials of suspected terrorists — at least of those captured in the U.S. — would thus force the release of people bent on mass murder.

"No civilized nation confronting serious danger has ever relied exclusively on criminal convictions for past offenses," Harvard Law School’s Alan Dershowitz, who has strong civil libertarian credentials, has written. "Every country has introduced, by one means or another, a system of preventive or administrative detention for persons who are thought to be dangerous but who might not be convictable under the conventional criminal law."

What the government should not be allowed to do, as Judge Brinkema held, is prosecute a man — let alone execute him — on a criminal charge that is disputed by witnesses in government custody whom the government refuses to make available. The administration’s brief in the appeals court complains that Brinkema’s ruling "would force the Executive to choose between either preventing future attacks through intelligence-gathering, or prosecuting completed attacks in the criminal-justice system." But the courts will not require testimony sought by Qaeda detainees unless it appears to be genuinely necessary to the defense. And in any event, the government will always have a perfectly adequate escape from any dilemma: detention as an enemy combatant.

Trial before a special military commission would also be an option, since the rules there would properly be less meticulously protective of defendants than the constitutionally mandated rules for ordinary prosecutions. But it would be fundamentally unfair for a military commission to deny a defendant any chance to present exculpatory testimony. It would be even worse to do so and then sentence him to death.

The Justice Department brief argues that foreign enemy combatants held by the U.S. overseas are beyond the power of the courts, and thus beyond the Sixth Amendment rights of the accused "to have compulsory process for obtaining witnesses in his favor." But the government’s refusal to make available witnesses who are within its complete control would deny Moussaoui a fair trial on those charges that the witnesses dispute. And the courts have the power and duty to prevent an unfair trial.

The Justice Department also offered Brinkema a written summary of statements by the captured Qaeda leaders to interrogators, as a substitute for videotaped deposition testimony. Such a summary might suffice in some circumstances, especially in a military commission. But the judge rejected the government’s summary in this case as "inaccurate and misleading" and said it "omits some exculpatory information reflected in the classified summaries."

That was a stunning indictment of the Justice Department. Only people privy to the classified interrogation summaries are in a position to evaluate whether it was justified. But from what’s on the public record, a neutral judge who is no mush-head has more credibility than any prosecutor (or defense lawyer). Especially prosecutors representing Ashcroft’s Justice Department, which once insisted that making public the names of any of the 1,100 people detained virtually incommunicado on immigration charges after 9/11 — even if they consented — would violate their privacy rights.