Article from CBS News by Rebecca Shabad.

Nearly a decade ago, FBI agents arrested a 24-year-old legal permanent resident from Afghanistan in the U.S. who was charged with conspiracy to bomb the New York City subway system.

A tool approved by Congress in 2008 helped federal officials catch this man, Najibullah Zazi, and prevent him from carrying out his plot. That tool is set to expire Dec. 31, and a debate has been brewing among lawmakers about where a reauthorization should fit on the spectrum of balancing broad surveillance powers and protecting individuals’ privacy.

To unravel the 2009 plot, officials relied on the authority provided by the Foreign Intelligence Surveillance Act’s (FISA) Section 702. They used it to expose an email address used by an al Qaeda courier in Pakistan, which revealed communications with an unknown person located in the U.S. who was seeking advice on how to build explosives. The National Security Agency (NSA) passed the information along to the FBI, which identified the man as Zazi. After he and his co-conspirators were arrested, the Privacy and Civil Liberties Oversight Board, an independent executive branch agency, said that, “Without the initial tip-off about Zazi and his plans, which came about by monitoring an overseas foreigner under Section 702, the subway bombing plot might have…succeeded.”

Congress is now wrestling with how to modify the program, last renewed in 2012, and dubbed the “crown jewels of the intelligence community” by former FBI Director James Comey. Documents leaked by former NSA contractor Edward Snowden in 2013 revealed that the government has used this capability to collect data, which has intersected with Americans’ communications.

Read the entire article at CBS News.