Communication spying of the PRISM variety [1] is exactly the kind of thing that should aid in the prevention of lone wolf style attacks. You're telling me that a modern lone wolf never uses a web search to find out "how to [buy an automatic rifle/how to rent a car anonymously/insert heinous act here]"?

If the surveillance is gathering up these searches and still has no record of stopping attacks, then two options, amongst others, are: get better filtering and analysis techniques, or my preferred option, disband the (illegal) programs.

[1] https://en.wikipedia.org/wiki/PRISM_(surveillance_program)#E...