Law enforcement officials could have something very different on their hands as they investigate the dual bomb blasts that struck the Boston Marathon finish line today: a potential abundance of photo and video evidence from the public.

Government surveillance, while growing, still misses more than it catches. But events with thousands of spectators offer the potential for a detailed crowdsourced record of what happened.

This public panopticon is changing how we see the world. February's Russian meteor was captured by many dash-cams mounted in Russian cars, but in this case the event is of profound interest to law enforcement officials, not just scientists.