U.S. customs officials apprehended a man accused of living illegally in the United States for more than three decades under an assumed identity, authorities said Thursday.

U.S. Customs and Border Protection (CBP) announced that officials arrested the man as he and his wife were trying to cross back into the United States in Texas at the Anzalduas International Bridge.

Officials did not name the man — and did not immediately respond to inquiries from LifeZette. (Shown above are two customs inspectors.)

“This interception of someone claiming to be a U.S. citizen and reaping benefits not entitled to them is a prime example of CBP’s intelligence-gathering capabilities and inspections experience,” Andres Guerra, port director, said in a statement.

“People need to realize that committing immigration violations do carry serious consequences and will be punished to the fullest extent of the law.”

CBP officials offered few details to explain why inspectors suspected the man of fraud.

They said an inspection officer referred the 57-year-old man for a secondary check. He showed a Texas driver’s license and claimed to be a U.S. citizen, and his wife presented a green card.

Officials said inspectors used biometric verification through CBP databases to confirm the woman’s identity — and then discovered the man to be a Mexican citizen. His U.S. birth certificate and Social Security card did not belong to him, according to the agency.

Authorities said further investigation determined that the ID belonged to another man — and that the suspect has used it to assume U.S. citizenship for more than 30 years.

It is unclear how many illegal immigrants may be living as American citizens under the cover of stolen documents.

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Jessica Vaughan, director of policy studies at the Center for Immigration Studies (CIS), said the number could be in the millions. She based that on an estimate by the Treasury Department that illegal immigrants have fraudulently used some 8 million Social Security numbers to obtain employment.

Vaughan said only a small percentage of people crossing the border get referred for secondary inspections. That was especially true during Barack Obama’s administration, she said.

“The mentality used to be the priority was to keep the line moving,” she said.

President Donald Trump’s administration has come under fire for revoking passports of U.S. citizens of Mexican heritage.

The government has denied that, casting the effort as an attempt to find people who fraudulently obtained citizenship.

Related: Border Protection Nabs Alleged Impostor with Facial Recognition Tech

“This is actually a different kind of case,“ Vaughan said. “But it’s very encouraging to see that CBP and the Trump administration are being empowered to go after cases like this.”

The administration has made a push to tighten borders.

After years of delay, airports have begun to install facial-recognition technology to compare travelers’ faces with their photo IDs.

In August, customs officials caught their first impostor using the new technology at Washington Dulles International Airport after it had been in place for only three days.

For more on facial recognition tech, see the video below: