Top U.S. intelligence officials appeared before Congress on Tuesday to detail what they claimed to be the role of NSA surveillance programs in foiling militant attacks. NSA Director Keith Alexander said more than 50 “potential terrorist events” have been thwarted, including 10 within the United States.

Gen. Keith Alexander: “In recent years, these programs, together with other intelligence, have protected the U.S. and our allies from terrorist threats across the globe to include helping prevent the terrorist — the potential terrorist events over 50 times since 9/11.”

Also testifying was FBI Deputy Director Sean Joyce. Joyce revealed two newly declassified cases he said were uncovered by NSA surveillance, one involving a group of men in San Diego convicted of sending money to a militant group in Somalia. The other was described as a plot to bomb the New York Stock Exchange.

Sean Joyce, FBI deputy director: ”NSA, utilizing 702 authority, was monitoring a known extremist in Yemen. This individual was in contact with an individual in the United States named Khalid Ouazzani. Ouazzani and other individuals that we identified through a FISA that the FBI applied for through the FISC were able to detect a nascent plotting to bomb the New York Stock Exchange. Ouazzani had been providing information and support to this plot. The FBI disrupted and arrested these individuals.”

Despite Joyce’s claims, the convict he named, Khalid Ouazzani, was never charged over a New York Stock Exchange bombing plot. Instead, Ouazzani pleaded guilty in 2010 to sending money to al-Qaeda. Joyce also cited the arrests of would-be New York subway bomber Najibullah Zazi and Mumbai bombing accomplice David Headley, an ex-informant for the DEA.

Sean Joyce, FBI deputy director: “In the fall of 2009, NSA, using 702 authority, intercepted an email from a terrorist located in Pakistan. That individual was talking with an individual located inside the United States, talking about perfecting a recipe for explosives. Through legal process, that individual was identified as Najibullah Zazi. He was located in Denver, Colorado. The FBI followed him to New York City. Later, we executed search warrants with the New York Joint Terrorism Task Force and NYPD and found bomb-making components in backpacks. … Also, David Headley, a U.S. citizen living in Chicago, the FBI received intelligence regarding his possible involvement in the 2008 Mumbai attacks responsible for the killing of over 160 people.”

Although the White House and lawmakers have repeatedly cited the cases of Zazi and Headley, some have questioned the role of NSA surveillance in their apprehension. Citing “court documents and interviews with involved parties,” The Guardian of London reported last week “data-mining through Prism and other NSA programs played a relatively minor role in the interception of the two plots.”