One way you could prevent more bomb attacks from happening is by catching the people responsible for this one. Besides that, I am not advocating CCTV everywhere, but downtown, or Subways, places that see extremely high throughput cannot be policed effectively by the police on their own. If you would say that maybe it's a good thing police cannot police everything, then how can you say police are necessary in the first place? They are supposed to be there to police, the cameras do the same thing better.

Somewhere else in this thread people were talking about drones. But that can happen right now, through private surveillance firms that would then sell information to the government. But then you're just lining some CEOs pocketbook instead of having a surplus. How is that a benefit?