In the aftermath of the killing of Osama Bin Laden by Navy Seals at a compound in Pakistan, the U.S. government has been very interested in examining the dwelling for all manner of intelligence, including how the Al Qaeda figurehead managed to communicate with the outside world without leaving a digital trail for U.S. government eavesdroppers to follow.

Using intermediaries and thumb drives, bin Laden reportedly managed to send e-mails in a circuitous but effective way. His manual process allowed him to become a prolific e-mail writer despite not having Internet or phone lines running to his compound.

His methods, described in new detail to The Associated Press by a counterterrorism official and a second person briefed on the U.S. investigation, frustrated Western efforts to trace him through cyberspace. The people spoke to the AP on condition of anonymity to discuss the sensitive intelligence analysis.

Bin Laden’s system was built on discipline and trust. But it also left behind an extensive archive of e-mail exchanges for the U.S. to scour. After killing bin Laden, Navy SEALs recovered about 100 flash drives that contained much of his e-mail communication, reported Mashable.

The trove of electronic records pulled out of his compound after he was killed nearly two weeks ago revealed thousands of messages and potentially hundreds of e-mail addresses, the AP learned.

At that location, the courier would plug the memory drive into a computer, copy bin Laden’s message into an e-mail and send it. Reversing the process, the courier would copy any incoming e-mail to the flash drive and return to the compound, where bin Laden would read his messages offline.