In the search for targets, the NSA has draped a surveillance blanket over dozens of square miles of northwest Pakistan. In Ghul’s case, the agency deployed an arsenal of cyber-espionage tools, secretly seizing control of laptops, siphoning audio files and other messages, and tracking radio transmissions to determine where Ghul might “bed down.”

The e-mail from Ghul’s wife “about her current living conditions” contained enough detail to confirm the coordinates of that household, according to a document summarizing the mission. “This information enabled a capture/kill operation against an individual believed to be Hassan Ghul on October 1,” it said.

The file is part of a collection of records in the Snowden trove that make clear that the drone campaign — often depicted as the CIA’s exclusive domain — relies heavily on the NSA’s ability to vacuum up enormous quantities of e-mail, phone calls and other fragments of signals intelligence, or SIGINT.

To handle the expanding workload, the NSA created a secret unit known as the Counter-Terrorism Mission Aligned Cell, or CT MAC, to concentrate the agency’s vast resources on hard-to-find terrorism targets. The unit spent a year tracking Ghul and his courier network, tunneling into an array of systems and devices, before he was killed. Without those penetrations, the document concluded, “this opportunity would not have been possible.”