In today's newest revelation, he also said the NSA monitored a known extremist in Yemen, who was in contact with an individual in the United States, Khalid Ouazzan, which led to detection of "a nascent plot to bomb the New York Stock Exchange."
Joyce also cited the case of David Headley, a U.S. citizen living in Chicago later convicted for his involvement in the 2008 Mumbai attacks in which more than 160 people died. Joyce said the NSA, through 702 coverage of an al Qaida-affiliated terrorist, found that Headley was working on a plot to bomb a Danish newspaper office that had published cartoon depictions of the prophet Muhammad.
"Lastly, the FBI had opened an investigation shortly after 9/11," Joyce said, without further identifying specifics of the potential attack. "We did not have enough information nor did we find links to terrorism, so we shortly thereafter closed the investigation.
"However, the NSA, using the business record FISA [Foreign Intelligence Surveillance Act], tipped us off that this individual had indirect contacts with a known terrorist overseas. We were able to reopen this investigation, identify additional individuals through a legal process and were able to disrupt this terrorist activity."
The House Intelligence hearing is ongoing. Check back for updates.