The six Guantanamo prisoners charged with participating in the 9/11 mass murders are "poster children for the death penalty," Attorney General Michael Mukasey told students in response to a question after a March 14 speech at the London School of Economics. True.

But Mukasey added a postscript: "In a way, I kind of hope from a personal standpoint — and I can say this because the military commissions will be run by the Department of Defense, not by the Justice Department, although we are participating with them … I kind of hope they don’t get it, because many of them want to be martyrs."

I kind of hope they don’t get it. Coming from the chief law enforcement officer of an administration that avidly supports the death penalty, especially for mass-murdering jihadists, this was a stunning assertion.

It was also a wise one. And I hope that it was not just an inadvertent slip into candor and common sense — a "gaffe," in Washington parlance. I hope that it was a strategically timed move to get the Bush administration to think things through, for once, and to slow down the jihadist-execution train before it gets too far down the track.

(Mukasey can be forgiven for adding an inartful analogy about "the masochist [who] says ‘Hit me’ and the sadist [who] says ‘No.’ ")

Of course, as Mukasey suggested, it’s hard to imagine a more deserving candidate for the death penalty than Khalid Shaikh Mohammed, who has admitted masterminding the 9/11 attacks and is proud of it.

But giving the terrorist murderers what they deserve makes no sense if the result would be to set back our war against jihadism. Aside from satisfying the jihadists’ mad lust for martyrdom, executions would also hurt us badly in the broader war by further inflaming anger at America across Western Europe and the Islamic world.

Such executions might well lead directly to retaliatory killings of Americans and indirectly to other horrors down the road. They would surely spur more young Muslims to become terrorists and would make governments abroad — especially in anti-death-penalty Europe — even more reluctant to help us catch and lock up terrorists.

So even if the death penalty saves innocent lives in civilian settings by deterring murders, as some experts argue, executing jihadist terrorists would have the opposite effect.

Why worry about this now? Because unless someone injects a dose of common sense into the lumbering, six-year-old military-commission process that is belatedly unfolding at Guantanamo, it may put us inexorably on track toward putting some or all of these evil men to death.

Military prosecutors charged the six suspected 9/11 conspirators in February with killing civilians and other war crimes and asked permission to seek the death penalty. But the Defense Department "convening authority" for the military commissions, former military Appeals Court Judge Susan Crawford, has not yet publicly decided whether to refer them to trial as capital cases.

If Crawford sets the death-penalty machinery in motion, it might prove unstoppable. Given the apparent weight of the evidence, it seems highly likely that the military jury or juries will convict and sentence one or more defendants to death, if they have that option. The military and civilian appeals courts and the U.S. Supreme Court might lack any legally plausible (or politically palatable) basis for overturning death sentences.

And the next president might face a no-win choice: allow executions to proceed and pay a terrible price abroad, or commute any death sentences and pay a huge political price at home.

Much of the world has already come to see Mohammed and his ilk less as the despicable mass murderers they are than as victims of American torture and abuse. And while the military-commission system has been much improved — gradually and grudgingly — since President Bush’s original, November 2001, quasi-kangaroo-court design, it remains unfair and illegitimate in the eyes of much of the world.

And so it will remain, at least for as long as Bush is president. Part of the reason is that the rules allow the introduction of evidence obtained by harsh and unreliable methods, perhaps including waterboarding, that many see as torture. Part of the reason is that these rules allow sharp restrictions on defense lawyers’ access to their clients and the evidence. Part of it is that they also allow use of hearsay and nonpublic classified evidence, which in my view is a justifiable concession to the unique difficulties of putting international jihadists on trial but which is much harder to justify when the penalty is death.

Besides, even if the military commissions turn out to be models of fairness, their identification with the widely reviled Bush will taint them in the eyes of most of the world. The former chief prosecutor at Guantanamo, Col. Morris Davis, who resigned in October, has argued that the trials have "a potential for rigged outcomes" that would ensure conviction. So what chance is there that world opinion will accept them as legitimate?

The military commissions’ dismal reputation, whether deserved or not, also bears on the hope expressed by some that the publicity generated by capital trials would refocus public attention on the monstrous brutality of the 9/11 attacks. To the contrary, experience so far suggests that as long as evidence extracted through abusive interrogation is used, and as long as the death penalty is on the table, the publicity would dwell at least as much on what was done to the defendants as on their suspected war crimes.

Consider the fairly typical, March 14 Associated Press article about pretrial hearings in three of the eight pending noncapital prosecutions at Guantanamo. The headline was, "Abuse Claims Complicating Gitmo Trials." The article stressed, "The military revealed the interrogator of one defendant had been convicted of assaulting an Afghan detainee who later died; a lawyer for the second charged his client was abused by a soldier known as ‘The King of Torture’; and the third boycotted his hearing after complaining of abuse in Afghanistan." The article barely mentioned the war crimes, in the 13th and 17th paragraphs.

What could we gain from sending Mohammed and his kind smirking to the execution chamber that would make the manifest international costs and risks worthwhile? If the idea is to make them suffer, condemning them to rot in isolation cells for the rest of their lives, with virtually no human contact, would be far more horrible than lethal injections or firing squads.

All in all, the heavy costs and minimal benefits of executing the 9/11 conspirators should be apparent to even the most ardent supporters of the death penalty — including President Bush — as well as to opponents and to those who (like me) have grave misgivings about capital punishment.

Would ruling out the death penalty for these prisoners make it pointless to go through the cost and difficulty of putting them on trial for their crimes, given that they will be detained indefinitely as dangerous "enemy combatants" in any event?

Perhaps so, as long as Bush is president. But criminal trials could serve important purposes if the next president and Congress first amend the military-commission rules to bar use of evidence obtained through highly coercive interrogation and to discourage use of the death penalty in any and all cases in which it would likely hurt us in the wider war.

Under those circumstances, criminal trials would demonstrate the justifications for imprisoning the 9/11 conspirators for life, under punitive conditions, far more convincingly than the slapdash "combatant status review tribunal" process that is currently used to justify indefinite detentions of suspected enemy combatants who have not been charged with crimes.

The next administration and Congress should also upgrade the detention process itself (see my May 12, 2007, column), to provide a more reliable basis for holding would-be terrorists who appear to be too dangerous to release but who cannot feasibly be proven guilty of any crime.

The 9/11 conspirators can, and should, be proven guilty of having committed crimes. The key is to do it in fair trials free of the distractions that come from using evidence obtained through abusive interrogations and from the specter of executions. That won’t happen during the Bush administration, which seems locked into a process that has already failed the test of world opinion.

So maybe it’s a good thing that the military commissions are still so mired in procedural challenges and delays that five of the six men who could face capital charges have not yet even been assigned military defense lawyers. Indeed, maybe some officials who understand the dangers of the current process have quietly decided that, for now, their best option is to stall.