The CIA's Illicit Transactions Group isn't listed in any phone book. There are no entries for it on any news database or Internet site. The ITG is one of those tidy little Washington secrets, a group of unsung heroes whose job is to keep track of smugglers, terrorists, and money launderers. In late 1998, officials from the White House's National Security Council called on the ITG to help them answer a couple of questions: How much money did Osama bin Laden have, and how did he move it around? The queries had a certain urgency. A cadre of bin Laden's...