Does the NSA Know How to Prevent Terrorist Attacks?

New Yorker contributor  Mattathias Schwartz explains why the N.S.A.’s metadata program has been ineffective in thwarting terrorist attacks. His article “The Whole Haystack” explores how the recent massacre in Paris—which, like many attacks in recent years, was perpetrated by people known to law enforcement—could have been prevented. Schwartz also details what may be the only instance where Section 215 of the Patriot Act—which allows the government to collect “books, records, papers, documents, and other items” that are “relevant” to “an authorized investigation”—directly led to a conviction in a terrorism case. The article appears in the January 26, 2015, issue of The New Yorker.