Experts say there has to be a legal basis to revoke a person’s residency status, and removal needs to be ordered by an immigration judge.

Khalil’s situation immediately drew international attention because of the reason he was detained, and because, according to his lawyer Amy Greer, he holds a green card, which allows individuals to live and work permanently in the United States.

Rubio’s letter notified DHS that he had revoked both targets’ visas, setting in motion plans for U.S. Immigration and Customs Enforcement to arrest and attempt to deport them, according to a senior DHS official and another U.S. official who spoke on condition of anonymity to describe how the operation against Khalil took shape.