One of Al Qaeda's first assignments for Iyman Faris, the Ohio truck driver named last month in a terrorist plot to destroy the Brooklyn Bridge, was to visit a travel agency while he was in Pakistan in late 2001 to have some old airline tickets reissued, federal investigators say.

Because the tickets were not in his name, Mr. Faris needed an explanation to validate his request. Investigators say he used one that other Qaeda recruits have relied on to disguise their intentions: he pretended to be a member of Tablighi Jamaat, a fraternity of traveling Muslim preachers that is well known in Pakistan and other Muslim countries.

Founded in rural India 75 years ago, Tablighi Jamaat is one of the most widespread and conservative Islamic movements in the world. It describes itself as a nonpolitical, and nonviolent, group interested in nothing more than proselytizing and bringing wayward Muslims back to Islam.

But since the attacks of Sept. 11, 2001, Tablighi Jamaat, once little known outside Muslim countries, has increasingly attracted the interest of federal investigators, cropping up on the margins of at least four high-profile terrorism cases.