Revealed: Why Snowden had access to so much sensitive information

It is a title that officials have carefully avoided mentioning, perhaps for fear of inviting questions about the agency’s aggressive tactics: an infrastructure analyst at the N.S.A., like a burglar casing an apartment building, looks for new ways to break into Internet and telephone traffic around the world.

That assignment helps explain how Mr. Snowden got hold of documents laying bare the top-secret capabilities of the nation’s largest intelligence agency, setting off a far-reaching political and diplomatic crisis for the Obama administration…

The N.S.A.’s assessment of Mr. Snowden’s case will likely also consider what has become, for intelligence officials, a chilling consideration: there are thousands of people of his generation and computer skills at the agency, hired in recent years to keep up with the communications boom.

The officials fear that some of them, like young computer aficionados outside the agency, might share Mr. Snowden’s professed libertarian streak and skepticism of the government’s secret power. Intelligence bosses are keeping a closer eye on them now, hoping that there is not another self-appointed whistle-blower in their midst.