We should be spying on the likes of Adam Lanza. We should stop being reactive... ie: stupid tighter gun controls that accomplish more harm than good because people are upset about a psycho with a gun... and become more preventive.
I don't think Lanza would have been helped by a surveillance state. The clues were already there, it was obvious that he had social problems. Do you think he was talking to people about his upcoming spree on his cellphone? Even if he was (and was caught) the system is for prosecution, not for psychological intervention. The system isn't used proactively at all, as a matter of fact, they simply go the database to obtain evidence to use against someone for whatever crime they are being charged with.
Therein lies one of the problems. The judicial system has become more focused on warehousing accused criminals by the bulk, however petty the offense may be or if at all, than it is about addressing problems with real solutions.
It doesn't help at all that the NYPD seems to continually put badges on morons to supposedly keep the streets safe.