If Big Brother is listening to everything was say and everything we do, why do we have crime?

[KurtNYC]

7. They record so they can find and play back calls later.

For example, after the Boston bombers are identified they can go back to the recordings of their phone calls and listen to all of them and see who they conspired with and then pursue the co-conspirators ASAP.

The problem in stopping crimes and terrorism is not with intelligence gathering. Bush was told 36 days before 9/11/01 in a daily briefing memo that "bin laden determined to strike within US" , specifically with airplanes. They had the hijack teams under surveillance. The intelligence community did their job. The failure was elsewhere in the chain.

Surveillance's primary role is identifying bad actors, before or after they commit whatever. Stopping them or catching them falls to others.