German agencies mounted a massive investigation of the suspects. Hundreds of police and intelligence officers watched them around the clock for months as they allegedly plotted and assembled large quantities of raw materials that authorities believed could be used to make explosives. At one point during the investigation one of the surveillance cars following the suspects had its tires slashed; German investigators concluded that the IJU suspects knew that they were being watched. Investigators were particularly alarmed that the suspects appeared to proceed with their plans anyway.

Shortly before German authorities believed the IJU plot was about to come to fruition, the counterterrorism officers staged a stealthy operation to neutralize the would-be explosives. They managed to sneak into the building where the suspects had stashed large quantities of high-concentrate hydrogen peroxide—a homemade bomb ingredient also used in hair bleach—and replaced it with identical containers of a harmless liquid. Gelowicz and a handful of other suspects were then arrested, and an international manhunt was launched for suspected co-conspirators, some of whom had allegedly fled to Turkey and at least one of whom was believed to be in Britain. Gelowicz is still in jail in Germany awaiting trial.

Counterterrorism officials in Europe and the United States say that Al Qaeda is not only seeking to recruit Western-born converts like Gelowicz as future terrorist operatives but also native Muslims who can pass for Westerners when going through security checkpoints. A German counterterrorism official told NEWSWEEK that German authorities are doing their best to track suspected militants going to and from the Pakistani border region. The problem: the most popular travel route for suspects is from Germany to Turkey and then via Iran to Pakistan, and it is very difficult for investigators to determine who among the hundreds of thousands of travelers might be planning an onward journey for terrorist training. (As Terror Watch reported last year, German authorities set up a special project to monitor dozens of suspects traveling back and forth between Germany and war-torn Iraq.)

British counterterrorism officials are also monitoring the huge volume of people who travel between the United Kingdom and Pakistan—an estimated 400,000 to 500,000 per year. British investigators have produced evidence showing that suspects in recent U.K.-based terrorist plots made trips to Pakistan for terrorist training. Among the suspects are British-born or British-raised operatives in several notorious terror plots, including the July 2005 bombings of London subway trains and a double-decker bus, a plot to bomb U.S. financial buildings, and a 2006 plot to bomb airliners crossing the Atlantic from Britain. The trial of several suspects in the airline bombing plot—reportedly including at least one British convert to Islam—is soon set to begin in London.

Other U.K.-born converts to Islam have been detained by antiterrorism investigators in the U.K. and Kenya. One of the most notorious British-born Muslim converts who subsequently became involved in an Al Qaeda plot was Richard Reid, a petty criminal from South London who unsuccessfully tried to blow up a transatlantic airliner in December 2001 using a bomb built into a shoe. Investigators believe Reid initially converted to Islam while serving time in a juvenile prison and that he later became more radical while attending extremist London mosques.

A handful of American converts to Islam have also become involved with Al Qaeda or related groups. The most prominent is Adam Gadahn, a.k.a. Azzam al-Amriki (Adam the American), a California native who has appeared frequently in Al Qaeda propaganda videos hurling bloodcurdling threats against the United States. Another well-known U.S. convert was John Walker Lindh, the so-called American Taliban, who was picked up in Afghanistan after American-led forces rousted the Taliban government there in the wake of 9/11. Lindh, who pleaded guilty to aiding the Taliban and is now serving a U.S. prison sentence, never made it into Al Qaeda's inner circles.