HOUSTON -- One evening two winters ago, a man in Staten Island, N.Y., absent-mindedly flipped through his mail. Inside one envelope was a stack of fake documents, including U.N. and Defense Department identification cards, and a note: "We would hate to have this fall into the wrong hands." It had. The package, intended for a member of a self-styled militia in New Jersey, had been delivered to the wrong address. From that lucky break, federal officials think they might have uncovered one of the most audacious domestic terrorism plots since the 1995 Oklahoma City bombing. Starting with a single piece...