WHEN THE government brought Ahmed Omar Abu Ali back to the United States from Saudi Arabia, there was every reason to expect his trial on terrorism charges to test the ability of U.S. courts to try cases laden with diplomatic and national security issues. Mr. Abu Ali, an American citizen, was arrested at the Saudi university at which he was studying. His family alleged that on behalf of the U.S. government, he was held for the better part of two years without charge or access to counsel. When his parents brought suit in this country, the government fought the lawsuit not only with secret evidence but with a secret legal theory. It then brought him home and charged him with plotting to kill President Bush and conduct major terrorist operations. Mr. Abu Ali, in turn, claimed that he had been tortured and had confessed falsely under duress -- an allegation that, given Saudi Arabia's human rights record, was plausible. Sorting out the question of his guilt and the linked question of his treatment seemed a tall order indeed.

Last week, a jury in federal court in Alexandria convicted Mr. Abu Ali on all charges against him. The trial, which was conducted remarkably smoothly, answered a lot of the troubling questions the case posed. It now appears, for example, that Mr. Abu Ali was not arrested at the behest of American authorities but on the initiative of Saudi authorities investigating terrorism in their own country. After a lengthy set of hearings on Mr. Abu Ali's allegations of torture, U.S. District Judge Gerald Bruce Lee produced a detailed opinion rejecting them and holding that Mr. Abu Ali's incriminating statements about his plans and activities were voluntary and, therefore, admissible as evidence against him. The jury evidently agreed. The trial had certain peculiarities; key witnesses testified from Saudi Arabia by videoconference. But in the main, the result is an outcome that has happened too infrequently in the war on terrorism: a conviction in a major case following the regular rules.

The Bush administration has often emphasized the difficulty of trying terrorism cases in federal court. Certain cases, like that of Sept. 11 conspirator Zacarias Moussaoui, have tended to validate the concerns. The result has been an instinct to seek alternatives: military commissions, for example, or long-term detention without trial.

But Mr. Abu Ali's case illustrates the benefits of proceeding whenever possible under the existing criminal justice system. At the end of a trial under the auspices of a conscientious judge, it's hard to see him as a victim of any particular civil liberties abuse at the hands of his own government. Rather, there is now a lengthy public record justifying his imprisonment.