A Wisconsin state patrol trooper who was detained by federal immigration agents at an airport has been released from custody, his lawyers said.

Agents approached Carel Aaron Van Der Merwe, a South African national, on Thursday as he waited to board a domestic flight. He moved to the United States at the age of 14 and has been waiting seven years for his asylum case to be heard. In the meantime he received permission to work, valid through 2030, and used it to serve in Wisconsin law enforcement.

The Department of Homeland Security defended the arrest, saying he had overstayed a visa issued in 2019 and that work permission or a pending application does not by itself confer legal status. His lawyers rejected that account, pointing out that another branch of the same department, the agency that handles citizenship and immigration services, had authorised him to work.

His legal team said on Friday that he would be freed but would have to wear an electronic monitor and check in regularly with immigration authorities. They welcomed the release while stressing that he must still argue his case before an immigration judge. The department did not immediately explain what prompted the decision to let him go.

Video from his graduation last year showed his father pinning on his badge in front of Wisconsin's governor. Van Der Merwe's family, who are white South Africans, arrived during Donald Trump's first term. After Trump returned to office they had reason to hope their claim would be viewed favourably, because the president signed an order saying the United States would promote the resettlement of Afrikaner refugees, citing claims of race based discrimination at home.

The arrest fits a wider pattern in which travellers with visas, residence papers or pending asylum cases have been stopped at airports as the administration pursues a mass deportation drive. Van Der Merwe's lawyers advised other noncitizens with unfinished immigration files to speak to an attorney before flying, even if they have travelled without trouble in the past.