Osama bin Laden sent thousands of emails to his various operatives around the world without Internet or a phone line at home, as he feared he would be discovered by the US government. The terrorist created a very painstaking system to pull of the feat, according to a counterterrorism official and a second person briefed on the US investigation cited by the Associated Press.

In his hideout, Osama bin Laden would type out his emails on his computer and save them to a thumb-sized flash drive. He then passed the flash drive to a trusted courier, who would proceed to a distant Internet café, presumably a different one every time. Once there, the courier would plug the memory drive into a computer, copy bin Laden's messages into emails, and send them to whoever his boss had specified. Reversing the process, the courier would copy any incoming emails to the flash drive and return to the compound, where bin Laden would read his messages offline.

For years, the system, which was built on discipline and trust, helped bin Laden stay in touch with his various contacts around the world. His enemies were unable to trace him because he did not leave any digital fingerprints behind.

The US always suspected bin Laden was communicating through couriers, but did not anticipate the breadth of his communications: Navy SEALs hauled away roughly 100 flash memory drives after they killed bin Laden earlier this month. Officials say they appear to still contain bin Laden's back-and-forth communications, including email addresses, phone numbers, and thousands of messages.