On Thursday, at the Aspen Security Forum—a $1,500-per-head conference held this week in the Rocky Mountains—the head of the National Security Agency (NSA) admitted that the spy agency had been overbroad in its acquisition of telephone data.

NSA Director General Keith Alexander told the assembled crowd at the Aspen forum that when President Barack Obama first took office in January 2009, he called out the agency on its blanket data collection practices.

“When the president first came on board, we had a huge set of mistakes that we were working through in 2009,” he told the audience, according to the New York Times, which is a sponsor of the event. “He said essentially, ‘I can see the value of these, but how do we ensure that we get these within compliance and that everything is exactly right?'"

At the president’s direction, the NSA then set up a “directorate of compliance,” an internal watchdog group to make sure that it wasn’t over-collecting and stayed within the confines of the law.

The interviewer, Pete Williams of NBC News, also asked Alexander about an allegation that NSA leaker Edward Snowden made in the last several weeks, that when he was at the agency, he had the capability to listen in on “anyone’s” phone calls. Alexander categorically denied that.

“One, we don’t have the technical capabilities,” he said. “We’re a foreign intelligence agency. To do that you’d have to have AT&T and everybody else’s networks, and we don’t. We’d have to go to them. One of the things that you look at with these servers—we don’t own and operate AT&T. We couldn’t compel them to listen to those phone calls. That would require a warrant and probable cause finding. Under FISA we wouldn’t have a reason to do that. That would [be for the] FBI. You couldn’t sit at my desk and do that.”

Alexander also emphasized the need for secrecy in its surveillance programs and capabilities.

"The reason we use secrecy is not to hide it from the American people, not to hide it from you, but to hide it from those who walk among you who are trying to kill you," he argued. "How do we do that? That's part of the debate. How do we protect you and your civil liberties and privacy and still get the terrorists?"

You can watch the entire discussion below: