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“In 2001, the intelligence community was totally unprepared for the challenge that we saw from al Qaeda. In the nine or 10 years since then, they have significantly transformed themselves. … They are light-years from where they were on 9/11.”

He suggested that couriers have led the United States to other terrorist bosses.

“The deadliest job in the world for a while was becoming the No. 3 guy for al Qaeda,” said Mr. Hoekstra, referring to the killing of the group’s operations chief, Mohammed Atef, and then the demise of others who succeeded him.

“We got the No. 3 guy about every three or four months. … Part of our strategy was going after their command-and-control structure. Going after their hierarchy. That’s been a priority. The intel community uses its full range of tools to go after these guys.

“I can’t get into which one is the most efficient in terms of identifying and getting actionable intelligence. But, clearly, whether it’s electronic or whether it’s couriers the way they pass information, if you can penetrate the communication network, it’s a great tool in identifying who the decision-makers are and where they are so that you can act on it.”

An intelligence official said that in the hunt for bin Laden, the most difficult task was the gumshoe detective work.

“The hard work is finding the courier once he has been identified,” the official said.

“This would include the positioning of the best and the most unobtrusive surveillance team, meaning people who look and talk like people in Pakistan.

“It would mean finding a safe house without raising suspicions. It would include the best in clandestine photography as well. A really good surveillant is hard to find.”