WASHINGTON >> The government’s broad programs to collect U.S. phone records and Internet traffic helped disrupt a 2009 plot to bomb the New York City subways, a senior U.S. intelligence official said.

But the assertion raises as many questions as it answers because court testimony indicated the subway plot investigation began with an email.

Over the past days, The Guardian newspaper and The Washington Post have revealed classified documents showing how the National Security Agency sweeps up phone records and Internet data in its hunt for terrorists. Those programs have come under criticism from civil libertarians and some in Congress who say they were too broad and collected too much about innocent Americans.

In one of those programs, the NSA’s collected daily records of millions of phone calls made and received by U.S. citizens not suspected of any wrongdoing.

On Thursday, Rep. Mike Rogers, R-Mich., who leads the House Intelligence Committee, credited that effort with thwarting a terrorism plot. But he did not elaborate.

The senior U.S. intelligence official who asserted Friday that the phone records program together with other technical intercepts thwarted the subway plot would not provide other details. The official was not authorized to discuss the plot publicly and requested anonymity.

Afghan-American Najibullah Zazi pleaded guilty in the 2009 plot, saying he had been recruited by al-Qaida in Pakistan.

The break in that case came, according to court documents and testimony, when Zazi emailed a Yahoo address seeking help with his bomb recipe.

At that time, British intelligence officials knew the Yahoo address was associated with an al-Qaida leader in Pakistan. That’s because, according to British government documents released in 2010, officials had discovered it on the computer of a terror suspect there months earlier.

Because the NSA and British intelligence work so closely together and so little is known about how the NSA monitors email traffic, it’s possible that both agencies were monitoring the Yahoo address at the time Zazi sent the critical email in 2009.

What’s unclear, though, is how the phone program aided the investigation, which utilized court-authorized wiretaps of Zazi and his friends.

Based on what’s known about the phone-records program, the NSA might have had an archive of all the phone calls Zazi had made, which might have helped authorities look for possible co-conspirators.

Because the phone program remains classified, however, it’s impossible to say with certainty how the program benefited the investigation.