The member of a militia group caught detaining hundreds of migrants at the U.S. Mexico border is now in FBI custody.

Larry Mitchell Hopkins, 69, was arrested on felony firearm and ammunition charges. Investigators say he is part of a militia known as the United Constitutional Patriots.

The group’s actions have drawn swift condemnation from the American Civil Liberties Union and others who have equated the group’s actions to kidnapping.

In a statement to CNN, a spokesman for the New Mexico Governor’s Office said this about the militia group

“They have absolutely not been authorized by our office or any other. We are actively working with the AG’s Office, state police and local police to determine what has gone on and what can and will be done. That migrant families might be menaced or threatened in any way, shape or form is completely unacceptable.”

A spokesman for the group defended their actions to the New York Times, saying what they do is legal.