Despite having no Internet access in his hideout, Osama bin Laden was a prolific email writer who built a painstaking system that kept him one step ahead of the U.S. government's best eavesdroppers.

His methods, described in new detail to The Associated Press by a counterterrorism official and a second person briefed on the U.S. investigation, served him well for years and frustrated Western efforts to trace him through cyberspace. The arrangement allowed bin Laden to stay in touch worldwide without leaving any digital fingerprints behind.