Robert S. Mueller, FBI Director, 7 Apr 08:

From 9/11 to 7/7: Global Terrorism Today and the Challenges of Tomorrow
.....We in the FBI are panning for gold. First, we have to determine in which streams we are likely to find gold. Which suspected networks? Which human sources? Which websites? Then, agents and analysts must take their pans and wade through the waters of intelligence, carefully searching for nuggets of gold amid streams of repetitive or irrelevant information.

The gold might be a phone number, or a name, or a receipt from a bank transaction. It will likely be hidden among thousands of other scraps of information. With deft, methodical sifting, we can separate the gold from the dross, as Dame Eliza would say. But as she also points out, gathering the intelligence is just the start. It then must be verified and connected to other intelligence. And even then we are only seeing part of the picture.

Our goal is to get as close as possible to having the complete picture. For the FBI, this means we often continue to collect information long after we have gathered enough evidence for prosecution. Once we have the threat under control, we use these cases as intelligence collection platforms. Our mission is not just to disrupt an isolated plot, but to thoroughly dismantle the entire network that supports it.....