New facial recognition technology at Washington Dulles International Airport nabbed an impostor trying to enter the country, Customs and Border Protection (CBP) officials said Thursday.

Authorities said the system, which had been in place only three days, flagged a 26-year-old traveler from São Paulo, Brazil, Wednesday. The man displayed a French passport and claimed to be a French citizen, according to the agency.

Officials said the customs officer used the device to confirm that the passport photo did not match the man. During a secondary examination by another CBP officer, the man’s demeanor changed, and he started acting nervous, according to the agency.

Officers searched the man and found his true Republic of Congo identification card hidden in his shoe (see accompanying photo).

Casey Durst, the director of the CBP’s Baltimore field office, touted the results of the new system.

“Facial recognition technology is an important step forward for CBP in protecting the United States from all types of threats,” he said in a statement. “Terrorists and criminals continually look for creative methods to enter the U.S. including using stolen genuine documents. The new facial recognition technology virtually eliminates the ability for someone to use a genuine document that was issued to someone else.”

The United States already collects fingerprints of foreigners who apply for visas and matches them to prints taken when those travelers enter through an airport or seaport. But citizens of 38 countries participating in the visa waiver program are exempt from that. Customs officials still collect their fingerprints when they enter but have no other record.

“The gap that it closes is [when travelers from] visa waiver countries don’t have their fingerprints in the system,” said Jessica Vaughan, director of policy studies at the Center for Immigration Studies (CIS). “So we don’t have anything to match it to.”

“It’s just another layer that prevents bad actors from gaming our increasingly effective system.”

Vaughan, a former consular officer at the Department of State, said a traveler from a visa waiver country might be caught if he used a passport stolen from someone who had been to the United States and had fingerprints on file. However, millions of people from those countries have passports but never have been to the United States, she said.

“Until now, we have not had a way to match the fingerprints,” she said. “This is a big deal. So many millions of travelers now come in under the visa waiver program.”

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Vaughan said this week’s arrest proves the system works. She said the technology is better than relying on humans to make judgments about whether people match the passports they are carrying.

“We’ve never had any way to detect them as accurately as facial recognition,” she said.

Vaughan said the technology, once it is in place nationwide, will help prevent people from staying after their visas expire because it will provide a record of when each person comes and leaves. But she said the bigger benefit involves national security.

It will be harder for terrorists to sneak into the county with stolen passports, Vaughan said. She added that it also will be harder for a terrorist to avoid raising flags. Until now, a terrorist in the country on a visa could send someone else with his passport to his home country. That exit would provide a record that the person had returned home. With facial recognition, though, it would detect an impostor trying to leave.

CBP officials maintain that the new technology offers convenience to travelers, while helping to catch impostors. Dulles is one of 14 airports to install the technology to expedite customs inspections. It went into effect at the airport on Monday.

Officials contend that the system is faster and more efficient, while providing better security.

The agency is assessing the use of biometric technology as part of a future end-to-end process, from check-in to departure, in which travelers use biometrics instead of boarding passes or IDs throughout the security and boarding processes.

Related: More Than 700,000 Foreigners Overstayed Their U.S. Visas in 2017

Officials recently expanded testing to include one checkpoint at the Transportation Security Administration (TSA) at New York’s John F. Kennedy International Airport. The federal government has talked about implementing a biometric for years; Congress mandated it since shortly after the 9/11 attacks.

But progress has been painfully slow. Vaughan said every traveler has a photo and passport. Facial recognition technology is unobtrusive.

“It’s just another layer that prevents bad actors from gaming our increasingly effective system,” she said.