President Obama should revisit the decision of his attorney general, Eric Holder, to try the five top al-Qaida plotters of 9/11, including Khalid Sheikh Mohammed, in a civilian court in the heart of New York City.

Every human being, no matter how reprehensible, deserves a fair trial. But it would be wiser to try these men under the military-commission system applied to other alleged war criminals, in a secure location, with full legal representation for the accused and press coverage. War is different from robbing a convenience store, or even murder, and there are many practical reasons to be concerned about prosecuting the 9/11 attacks on America — which targeted national symbols and killed thousands of civilians and soldiers — as civilian crimes.

Under Mr. Holder’s plan, security will be an incredibly costly nightmare. (New York is already a top terrorism target, but imagine the publicity bonanza for terrorists disrupting the trial!) Jurors will fear assassination attempts. The trial will inevitably turn into a years-long propaganda opportunity for these zealots, preaching hatred of America and surely whipping up more hostility in radical Islamic circles than a quicker trial in military court would.

Rules of evidence are different in a civilian trial than in a military one. A judge in civilian court could conceivably throw out the cases because Mr. Mohammed and company were not read their Miranda rights before they were first questioned. Rock-solid evidence against them might be thrown out because of the way that evidence was obtained.

Most ominously, such a trial could, through the legal process of discovery, pry open to the eyes of al-Qaida and other enemies of America our means of obtaining top-secret information. (In the four-year-long trial of Zacarias Moussaoui, the so-called 20th hijacker who was arrested in the United States, America faced a decision of either dropping the charges or releasing intelligence secrets; fortunately, Moussaoui pleaded guilty before that decision was made.) And such a trial could well bring retribution down on the heads of those who worked conscientiously to protect America in the wake of 9/11, making it harder to find such people to protect America the next time around.

Rhode Island’s Sen. Jack Reed said he supports a civilian trial, because Mr. Mohammad will come across as a common criminal rather than a “holy warrior” and the U.S. Constitution will gain stature by trying the al-Qaida suspects as if they were U.S. citizens. It would be nice to think so, but the certain costs and risks almost surely outweigh those potential propaganda benefits.

Even if the five were released by the court, America could seize them all over again, Senator Reed promised. “They can be detained, and they will,” he said. We are not so sure.

A more secure and pragmatic approach would be to try them (fairly) in a military court.