All they really need is metadata, IP-addresses, then they can use network theory to build graphs that shows who is communicating with who. If you for example vi

All they really need is metadata, IP-addresses, then they can use network theory to build graphs that shows who is communicating with who. If you for example visit a "terrorist" web site you are now linked to everyone else who also visited that site. Using network mesh graphs they can discover new "terrorist" cells. They can even figure out who the leader of this "terrorist" cell is and effectively destroy the cell. I can imagine they are also tracking location data to see who meets physically.