By JOHN SULLIVAN and JOSEPH NEFFRaleigh News & ObserverNovember 13, 2001 FORT BRAGG, N.C. - A former sergeant at Fort Bragg who became a close adviser to Osama bin Laden obtained sensitive documents describing how U.S. special operations units function. Ali A. Mohamed, a trusted trainer in bin Laden's al Qaeda network, walked the halls of the U.S. military's top warfare planning center at Fort Bragg for more than two years as an Army sergeant. From 1987 to 1989, he acquired sensitive documents describing how special operations units work and a detailed plan for a special operations training exercise, court ...