The Boston Bomber Brothers had been identified and apprehended by "spying" before they killed and wounded innocents?
That would be impossible absent a warrant to investigate and detain.
This goes to the ignorant idiocy of the entire spying non-issue.
The surveillance programs do not constitute law enforcement, the intent is to gather information, not pursue criminal prosecutions because none of the evidence would be admissible in court without a warrant.
LOL... riiiight.