PAUL RATJE via Getty Images United Constitutional Patriots members Jeff Allen, Jim Benvie, "Viper" and "Stinger" take a cigarette break while patrolling the U.S.-Mexico border in Sunland Park, New Mexico, last month.

FBI agents arrested a leader of a heavily armed right-wing militia on Saturday in New Mexico just days after the vigilantes posted a video of members “detaining” hundreds of immigrants, many of them children.

Larry Mitchell Hopkins, 69, of the United Constitutional Patriots militia, was arrested on a “federal complaint charging him with being a felon in possession of firearms and ammunition,” according to an FBI statement.

“This is a dangerous felon who should not have weapons around children and families,” New Mexico Attorney General Hector Balderas said in a statement following the arrest. The FBI action “indicates clearly that the rule of law should be in the hands of trained law enforcement officials, not armed vigilantes.”

The FBI busted Hopkins in Sunland Park, where the militia is headquartered, with the help of local police, NBC reported. Balderas identified him as a member of the militia detaining immigrants. According to the Southern Poverty Law Center, Hopkins has identified himself as the “national commander” of the UCP. According to court records, Hopkin has been convicted of felony firearm possession and impersonating an officer, The Daily Beast has reported.

Hopkins, a sometimes performer, also goes by the name of the late singer Johnny Horton Jr.

“Johnny” often runs the militia’s radio program. In a segment last month, he appealed for more “boots on the ground” to “capture” immigrants. He pleaded for donations for the group. “We’re down to nothing,” he said.

His arrest came just two day after the American Civil Liberties Union alerted Balderas and New Mexico Gov. Michelle Lujan Grisham in a letter that an “armed fascist militia organization” was working to “kidnap and detain” asylum-seekers at gunpoint in the state. The group had posted a video Tuesday showing hundreds of detained immigrants, many of them children. A woman with the militia can be heard telling others not to point guns at the migrants as they wait for U.S. Border Patrol agents to arrive.

“The Trump administration’s vile racism has emboldened white nationalists and fascists to flagrantly violate the law,” the ACLU said in the letter.

The governor on Friday called on the militia to stand down. “Regular citizens have no authority to arrest or detain anyone,” Grisham said Friday.