WASHINGTON — Using intermediaries and inexpensive computer disks, Osama bin Laden managed to send e-mails while in hiding, without leaving a digital fingerprint for US eavesdroppers to find.
His system was painstaking and slow, but it worked, and it allowed him to become a prolific e-mail writer despite not having Internet or phone lines running to his compound.
His methods, described by a counterterrorism official and a second person briefed on the US investigation, frustrated Western efforts to trace him through cyberspace. The people spoke 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 United States to scour.
The trove of electronic records pulled out of his compound after he was killed last week is revealing thousands of messages and potentially hundreds of e-mail addresses.
Holed up in his walled compound in northeast Pakistan with no phone or Internet capabilities, bin Laden would type a message on his computer without an Internet connection, then save it using a thumb-sized flash drive. He then passed the flash drive to a trusted courier, who would head for a distant Internet cafe.
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.
Navy SEALs hauled away roughly 100 flash-memory drives after they killed bin Laden, and officials said they appear to archive the back-and-forth communication between bin Laden and his associates around the world.
The Justice Department is already coming off a year in which it significantly increased the number of national-security letters, which allow the FBI to quickly demand information from companies and others without asking a judge for a subpoena.
The cache of electronic documents is so enormous that the government has enlisted Arabic speakers from around the intelligence community to pore over it.