If the NSA spy program is so damn effective, how could they possibly have missed this one?
I think it's because they deliberately turned a blind eye to Mosques. They didn't start looking into Boston Mosques until several days after the bombing, and they skipped the one these terrorists went to entirely. So, they watch me and thee, but not the people most likely to commit terrorism. What can go wrong?
The NSA spy program is looking at the forest. Tsarnaev brothers and Nidal Hassan were individual trees, to be protected by political correctness.