At a hearing last week, NSA head Keith Alexander very carefully explained that his agency was not currently gathering location data on Americans under one particular program. Because, as a statement released Wednesday indicates, they stopped collecting that data in 2011 — and won't rule out doing it again.

The New York Times reports there was a pilot program under which the agency did indeed gather location data from Americans' cell phones:

An official familiar with the test project said its purpose was to see how the locational data would flow into the N.S.A.'s systems. While real data was used, it was never queried as part of any investigation, the official said. It was unclear how many Americans’ locational data was ingested as part of the project or whether the N.S.A. has held onto that information.

The Times indicates that the agency pulled data in 2010 and 2011. It also quotes a statement from Oregon Sen.r Ron Wyden, whose pressure on Alexander led to last week's cautious response. "[O]nce again," it reads, "the intelligence leadership has decided to leave most of the real story secret — even when the truth would not compromise national security."

During a hearing of the Senate Judiciary Committee on Wednesday, Alexander gave more detail when asked by Texas Sen. Ted Cruz what other data related to citizens the NSA thinks should be collected. "I can't think of any right now," Alexander said. But he didn't really slam the door on collecting geolocation data again in the future.

"I do think as we look at the phone data, we're going to have to look at how that changes as we bring mobility in, and that's been the question of it. So we released to the Intel committees today clarification so they understood the difference on locational data and those requirements."

"I do think that we're going to have to evolve as the threat evolves.

Do you believe, Cruz followed up, that the NSA needs to collect geolocation data on citizens to prevent terrorism? Alexander read the statement obtained by the Times, including outlining how any additional acquisition could go forward. He then continued:

"I would just say that this may be something that is a future requirement for the country, but it is not right now because when we identify a number, we can give that to the FBI. When they get their probable cause, then they can get the locational data that they need. And that's the reason that we stopped in 2011."

To parse that last sentence: When the NSA gets a request for data on someone from the FBI — or when the NSA comes across evidence that someone in the United States is possibly involved in a crime — it works with law enforcement to share the information it has collected. What Alexander is saying is that the FBI can get that location data via a search warrant. But what he is also saying is that the ability of the FBI to pull data is why the pilot program ended — not just because they were done "testing" how that data could work in their database.

The Times notes another reason the NSA may have curtailed collecting that data.

[I]n 2012, the [Supreme Court] ruled that the police’s use of a G.P.S. tracker attached to a suspect’s car violated Fourth Amendment privacy rights. The case turned on the fact that the police had to trespass on the suspect’s property to attach the device, but five justices separately suggested that any long-term, automated collection of a person’s public movements might raise Fourth Amendment issues.

It would not be the first time the NSA crossed that constitutional line.