The Federal Bureau of Investigation has taken over an investigation into a suspicious letter discovered at the Guam Visitors Bureau's office in Tumon. Just before 9 this morning GVB general manager Karl Pangelinan says a member of his staff opened a letter that was handwritten and dually addressed to the Guam Visitors Bureau and the mayor's office.Pangelinan told KUAM News, \It was just natural for our staff to go ahead and open it and when they opened it