In slide made public by the newspapers, NSA analysts were encouraged to use data coming from both Prism and from the fiber-optic cables.
Prism, as its name suggests, helps narrow and focus the stream. If eavesdroppers spot a suspicious email among the torrent of data pouring into the United States, analysts can use information from Internet companies to pinpoint the user.
With Prism, the government gets a user's entire email inbox. Every email, including contacts with American citizens, becomes government property.
Once the NSA has an inbox, it can search its huge archives for information about everyone with whom the target communicated. All those people can be investigated, too.
In that way, Prism helps justify specific, potentially personal searches. But it's the broader operation on the Internet fiber optics cables that actually captures the data, experts agree.