The German IJU investigation began about a year ago when U.S. intelligence agencies eavesdropping on international communications spotted suspicious message traffic, believed to include e-mails, between Pakistan and Germany. U.S. authorities alerted German intelligence to the suspicious messages, and the Germans opened an investigation. A few weeks later, around Christmastime, the investigation intensified after suspects in the case were observed driving in suspicious patterns near a U.S. military installation in the Frankfurt area.

German investigators concluded that they had discovered a militant cell of the IJU, led by Gelowicz. A convert to Islam, he had taken a leadership role at an Islamic center in the town of Neu Ulm in southern Germany three years earlier, after the center's militant Egyptian imam was deported. Last year, according to investigators, Gelowicz and two other principal suspects traveled to remote tribal areas on Pakistan's border with Afghanistan. There, authorities believe, the three underwent indoctrination and weapons training in camps operated by the IJU, a group that had split from a larger Islamist movement in Uzbekistan and affiliated itself with the fugitive Al Qaeda leadership, which is believed to be hiding out in the same region. Officials say they do not have evidence that the German suspects were in direct contact with Osama bin Laden or his inner circle.

Upon their return to Germany, investigators told NEWSWEEK, Gelowicz and his cohorts began conducting none-too-subtle surveillance of potential American targets, many in the Frankfurt area. They also allegedly recruited and indoctrinated other potential members of their cell. Some of the new recruits were sent off to Pakistan for training (including the five suspects who are currently being sought there). Investigators read e-mail traffic between the suspects in Germany and people they believed to be IJU contacts in Pakistan discussing plans for possible attacks on U.S. targets in Germany.

German authorities believed that Gelowicz and his cell in Germany were taking orders related to the plot from IJU leaders in Pakistan. The Germans still are trying to uncover the real identities of the IJU leaders in Pakistan—whom they believe were pulling the strings in the plot. Authorities believe the IJU leader in the case goes by the nom de guerre "Sousa" but say they do not know his true identity.

Over the last nine months, German authorities mounted a massive surveillance operation of IJU-plot suspects which, at one point, involved as many as 400 federal and local police officers and two or three hundred more intelligence officers. Investigators watched as the suspects purchased large quantities of high-concentrate hydrogen peroxide, a household chemical used to bleach hair but also an increasingly common ingredient in homemade explosives. Sympathizers in Turkey were allegedly tasked with acquiring detonators. Investigators read e-mails and listened in on conversations—including discussions in a bugged car—as suspects talked about attacking an unnamed airport, U.S. military installations and restaurants and nightclubs frequented by Americans. The suspects allegedly researched potential targets over the Internet using Google Earth.

During the course of the investigation, it became clear that some of the central suspects knew authorities were on to them. On at least one occasion, a German official said, suspects slashed the tires of a vehicle counterintelligence officers were using to follow them.