“This is a dangerous felon who should not have weapons around children and families."

Paul Ratje / AFP / Getty Images Members of the United Constitutional Patriots speak inside the group's camper in Anapra, New Mexico.

The FBI arrested the head of an armed right-wing "patriot" group that had detained hundreds of migrants at the New Mexico border on Saturday for being a felon in possession of a weapon. Larry Mitchell Hopkins, 69, was arrested on a federal complaint charging him with being a felon in possession of firearms and ammunition, the FBI said. He was arrested near the New Mexico border with the assistance of the Sunland Park Police Department.

The arrest of Hopkins, who is referred to as "the commander" of the United Constitutional Patriots and goes by the alias Johnny Horton Jr., was hailed by New Mexico Attorney General Hector Balderas. “This is a dangerous felon who should not have weapons around children and families,” Balderas said in a statement. “Today's arrest by the FBI indicates clearly that the rule of law should be in the hands of trained law enforcement officials, not armed vigilantes.”

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The Flora Vista, New Mexico, resident was previously arrested in 2006 in Klamath County, Oregon, facing charges for impersonating a peace officer and two charges of a felon in possession of a firearm, according to court records. He ended up pleading no contest to a charge of impersonating a peace officer and guilty to felony possession of a firearm. Hopkins is expected to make his first court appearance in US District Court in Las Cruces, New Mexico, on Monday morning. Chuck Davis, head of intelligence for the militia, posted on Facebook that Hopkins, who he referred to as "the commander," had been arrested at base camp. "They set him up they are trying to use his past from 50 years ago," Davis said. "The commander needs all patriot [sic] to come to his aid." United Constitutional Patriots came under scrutiny this week after the group posted videos of its members detaining large groups of migrants near the border city of Sunland Park, New Mexico. The footage depicted militia members detaining people, many of them children, while armed. Members of the group have been camped near the border since November, hoping to shut off the flow of immigrants crossing the border, which they have described as an "invasion," echoing the hardline rhetoric by President Trump. Leaders say in that time they've detained more than 3,000 migrants.

Paul Ratje / AFP / Getty Images Dozens of people who had just crossed the US–Mexico border are detained in Sunland Park, New Mexico, by the United Constitutional Patriots.