With the growing scrutiny of government databases and the extent of domestic surveillance, new questions are being raised about a program FBI Director Robert Mueller once said could pull in emails from U.S. citizens on domestic soil “as they come in.”

Mueller’s comments came during a routine Senate Judiciary Oversight Committee hearing in March 2011.

He said “technological improvements” to an existing database meant the agency would not miss important investigative leads found in email traffic.

Mueller made the comment when testifying about intelligence failures that contributed to the 2009 Fort Hood massacre including email exchanged between accused shooter Army Maj. Nidal Hasan, an American citizen on U.S. soil, and cleric Anwar al-Awlaki, a known overseas terrorist who was targeted and killed in 2011 by the CIA.

As part of its ongoing investigation of the cleric, Fox News confirmed Awlaki was using at least 60 email accounts to connect with Hasan and other followers.

“Going forward, which is all we need to be concerned about at this time, what can you tell us about new procedures that are in place that will head off another Fort Hood in the future?”  then-Wisconsin Democratic Sen. Herb Kohl asked at the 2011 hearing.

Mueller replied: “We put in place technological improvements relating to the capabilities of a database to pull together past emails and future ones as they come in so that it does not require an individualized search.”

After classified National Security Agency documents were leaked earlier this month by contractor Edward Snowden, much of the recent debate has centered on the U.S. government’s ability to access Internet communications and whether it can gain “direct access” to the email stream -- a charge Internet providers have denied.

“We were as shocked about those revelations as anyone,” Google chief legal officer David Drummond told Fox News last week. “There's no lockbox, there's no backdoor -- none of the other terms that you've seen in the past few days. We comply with orders. We deliver information when we receive these targeted orders."

When the NSA was recently asked whether the database to which Mueller referred is part of or separate from the agency’s PRISM program that collects foreign Internet communications, the agency referred Fox to the FBI.

The bureau’s media office has so far declined to comment, saying it is reviewing Mueller's testimony.

Whistleblower Bill Binney, who spent four decades at the NSA, thinks Mueller is referring to "upstream" collection that cannot be explained by a legal order from a national security court.

"What he (Mueller) means when he says 'as they come in' is the near real time collection," Binney explained.

He also said the collection appears to include email originating in the United States to an overseas email account.

Binney said a Foreign Intelligence Surveillance Act order does not explain the existence of the database nor apparent real-time collection.

"It's not in the FISA laws,” he said. “It could be in the secret interpretation of section 215.”

(That section is the so-called business-records collection provision of the Patriot Act, the post 9/11 law that allows aggressive data surveillance to foil terror plots.)

Wisconsin Republican Rep. Jim Sensenbrenner helped draft section 215 but now doesn’t support its wide interpretation under the Obama administration.

“The recently released FISA order … could not have been drafted more broadly,” he wrote in an op-ed piece for The Guardian, which with The Washington Post broke the recent NSA stories.