Updated at 4:03 p.m. ET
Some Americans have been trailed and closely monitored by undercover air marshals as they traveled on U.S. flights, as part of a previously undisclosed Transportation Security Administration program called Quiet Skies. The marshals take notes on the targeted traveler's behavior, sending detailed reports to the TSA.
The existence of the program was first reported Saturday by the The Boston Globe, citing an internal TSA bulletin from March as well as anonymous sources within the department. The document leaked to the Globe says the program specifically targets travelers who are not on terrorist watch lists and are not under investigation by any agency.
Some air marshals involved have expressed misgivings about the domestic surveillance program, questioning whether it's legal and whether it's an efficient use of resources, the newspaper reports.
In a statement to NPR on Monday, the TSA defended the program as "a practical method of keeping another act of terrorism from occurring at 30,000 feet."
Spokeswoman Michelle Negron said the program "doesn't take into account race and religion, and it is not intended to surveil ordinary Americans."
The program is routinely reviewed by "legal, privacy and civil rights and liberties offices," she said.
The program began in 2010, with a new iteration in 2012 and a new "concept of operations" in March of this year, Michael Bilello, assistant administrator of public affairs for TSA, tells NPR. The document leaked to the Globe was connected to the March update.
Under the program, the Globe reports, "thousands of unsuspecting Americans have been subjected to targeted airport and inflight surveillance, carried out by small teams of armed, undercover air marshals."
The air marshals observe the targets and keep notes, the Globe reports — documenting whether they change clothes or shave while traveling, abruptly change direction while moving through the airport, sweat, tremble or blink rapidly during the flight, use their phones, talk to other travelers or use the bathroom, among many other behaviors.
The TSA's Bilello says that the detailed observation of behavioral patterns is not unusual for the agency. "Observation is something all TSA officers are trained in," he said. "So when you go to a checkpoint in the airport — you, me, everyone — our behavior is being observed.
"So ... federal air marshals that are observing an individual we're concerned about, based on travel patterns and other information ... of course they're watching their behavior. They're trying to determine, is this person going to take any action on a plane?"
Bilello confirmed that passengers do not need to be on terror watch lists, or suspected of any crime, to be monitored.
"These are people who perhaps haven't done anything previously to put them on a terrorist watch list, but perhaps there are things ... that make us concerned about their future activities or actions," he said.
The first red flag is foreign travel — specifically, frequent visits to "countries that we know have a high incidence of adversarial actions," as Bilello put it.
After analyzing travel patterns, the TSA pulls intelligence from a number of sources — state and local law enforcement, federal agencies and international partners — before deciding to assign an air marshal. The program is designed to ignore people clearly traveling for business or to visit family, and focus on potential threats, Bilello said.
The TSA would not provide details on the precise criteria required to flag a passenger for the program. Documents provided to the Globe suggest that reservations using the phone numbers or email addresses of watch-listed individuals are a consideration. According to DHS documents, Customs and Border Protection uses biographical data and outstanding warrants to conduct traveler risk assessments, and also has access to FBI facial recognition software.
The Globe reports that a flight attendant and a federal law enforcement officer are among those who have been flagged for surveillance under the program, to the frustration of air marshals who felt they were wasting their time.
Dozens of people are followed and observed each day, the newspaper says. According to the leaked memo, passengers in the Quiet Skies program remain on the list to be monitored for up to 90 days or 3 observed trips, whichever comes first.
The resulting reports are retained by the Department of Homeland Security, but not generally shared with other agencies, Bilello says; the TSA does not consider itself an intelligence-gathering organization.
Jonathan Turley, a professor at George Washington University Law School, tells NPR that whether or not Quiet Skies is legal depends on how exactly it is carried out.
In general, he says, people in public — on an airplane, for instance — do not have a reasonable expectation of privacy under the Constitution. "If other citizens can see you, the government and the police are allowed to see you," he told All Things Considered on Sunday. "They're also allowed to keep notes on what they observe."
But it's possible that the program could step over the line, he says.
"If [air marshals] are trying to see what's on the screen of a computer or take more intrusive steps, it could raise serious privacy issues under the Constitution," Turley said. "Also, if they're using these types of digital dossiers to restrict people, putting them on flight lists or putting them under some type of other limitation, that could also raise a serious matter under the Constitution. We simply don't know."