At a meeting held in a tightly guarded, bug-free conference room at Homeland Security headquarters last week, the chiefs of the sprawling department's major divisions briefed Ridge on some of the less-publicized measures taken. Biological weapons sensors had been deployed around sites of Christmas and New Year's college football games, including the Rose Bowl and Orange Bowl. "Plume modeling" tests to detect possible chemical weapons were conducted in New York area tunnels. New computer tests were conducted to track potentially suspicious immigrants and visitors to the United States. Investigators, for example, reviewed data on foreign-born graduate students in the Las Vegas area after intelligence (all of it quite vague) came in suggesting that city might be a target. (Those who were pursuing certain "technical" areas of study received extra scrutiny.)

But it is still far from clear whether any of these measures made any difference at all. No evidence of any chemical or biological weapons turned up; the only "hit" from all the radiation detectors came when technicians traced the source of the radiation to a homeless man's storage locker. (The radiation source turned out to come from a harmless radioactive metal commonly used in medical treatments.) There was initially some concern that a passenger whose name appeared on a U.S. government watch list did not show up for an Air France flight mentioned in intelligence reports as a possible hijack target. But U.S. intelligence ultimately concluded the man did not pose a serious threat-and no actual attack was averted.

In short, Homeland Security officials acknowledge that hard evidence may never turn up to prove that the Orange alert stopped a terror attack. Ridge said it may take months to get a handle on the quality of the intelligence that spooked the country. For his part, FBI Director Robert Mueller told reporters today the bureau was also still reviewing the reliability of the intelligence that prompted the higher Orange alert. As for the decision to move to Code Orange, Mueller said, "there is substantial reason to believe that heightened security deters attacks." But he also made it clear that the danger is far from over. "Al Qaeda is known to be fluid in setting the timing of attacks," he said, adding that there was still "substantial concern" that the terrorist group may yet launch a strike.

IS A 9/11 TRIAL IN THE OFFING?

For more than a year, nothing has been heard from the Bush administration about a matter that has long puzzled counterterrorism officials. Given that the United States has captured most of the key perpetrators of the September 11 plot, starting with the attacks' architect, Khalid Shaikh Mohammed, will they ever be put to trial?

But today, Mueller, in his briefing for reporters, offered the first glimpse that one might actually occur-and that if it did, it is likely to be before a military tribunal rather than in a U.S. courtroom. Asked by NEWSWEEK today if he would like to see such September 11 players as Mohammed and Ramzi bin al-Shibh (another key plotter who was captured more than a year and a half ago in Pakistan) ever put on trial, Mueller at first sought to beg off-and then responded: "Yes ... I would expect there will be some tribunals at some point." Mueller also said that the bureau has taken steps to "assemble the evidence" that might be used at such a trial.