President Obama addressed the US government's controversial domestic surveillance programs on Friday, justifying them in part because of his assessment that "they helped us prevent terrorist attacks," but without mentioning any specific incidents to back up that claim. Now, Reuters and The New York Times cite anonymous government officials who say that the PRISM program helped foil one attack in particular.

In 2010, Najibullah Zazi pled guilty to plotting an attack on the New York subway system using explosive devices. He was arrested in September 2009, after emailing the phrase "The marriage is ready" to an accomplice to signify that an attack was in the offing. The US and UK governments reportedly intercepted Zazi's email, leading to his arrest shortly after that message. According to New York Times and Reuters sources, the PRISM program was what allowed them to obtain that email, with an unnamed "senior intelligence official" specifically telling the Times that PRISM was the only way it could obtain those communications. "It was through an e-mail correspondence that we had access to only through Prism," said the individual.

We're not sure if that's accurate, though. Citing several sources from the time of Zazi's 2009 arrest and 2010 conviction, BuzzFeed reports that the FBI and UK government appear to have already had access to the email of Zazi's co-conspirator, Abid Naseer, after arresting him in Pakistan several months earlier. In November 2009, The Telegraph reported that a suspect's account was already being monitored at the time Zazi's message arrived. "The alleged plot was unmasked after an email address that was being monitored as part of the abortive Operation Pathway was suddenly reactivated," the publication wrote at the time. While the piecemeal accounts aren't totally clear, it throws doubt on the notion that Prism was responsible for preventing Zazi's intended crime.