GREENBELT, Md. (AP) — A former Canadian Armed Forces reservist plotted with other members of a white supremacist group to carry out “essentially a paramilitary strike” at a Virginia gun rights rally, a federal prosecutor said Wednesday.

U.S. Magistrate Judge Timothy Sullivan agreed to keep Patrik Mathews, 27, detained in federal custody pending a Jan. 30 preliminary hearing.

Mathews leaned back in his chair and quietly laughed when the magistrate read aloud a transcript of a video in which the Canadian national advocated killing people, poisoning water supplies and derailing trains.

“This is a very dangerous person,” the magistrate said during Mathews’ detention hearing in Maryland. “He espouses very dangerous beliefs.”

Later Wednesday, Sullivan refused to set bail for another defendant arrested in the FBI’s investigation of The Base. A prosecutor described William Garfield Bilbrough IV — a 19-year-old pizza delivery driver who lives with his grandmother in Denton, Maryland — as a leader of the group who was seen as a “prophet” by Mathews and the third man arrested in the case.

Assistant U.S. Attorney Thomas Windom showed the judge a photograph recovered from Bilbrough’s phone that shows him holding up the severed head of a goat he had killed in a “ritual sacrifice” at a training camp in Georgia for members of The Base. Bilbrough initially tried to kill the goat with a knife but failed, so he borrowed a gun to shoot it, Windom said.

Mathews, Bilbrough and Brian Mark Lemley Jr., 33, of Elkton, Maryland, were arrested Thursday on federal felony charges in Maryland and Delaware, just days before the pro-gun rally in Virginia’s capital. Federal prosecutors said in a court filing Tuesday that a hidden camera captured the men discussing “the planning of violence” at the rally and expressed hope that bloodshed could start a civil war. Monday’s event attracted tens of thousands of people and ended peacefully.

“This is a domestic terrorist investigation,” Windom said Wednesday.

Bilbrough, the only defendant in the case who isn’t facing firearms-related charges, participated in their early discussions about traveling to Richmond but recently had tried to distance himself from the group, the prosecutor said.

“He left The Base because he found out certain information about the leader of The Base,” Windom said without elaborating,

Bilbrough’s attorney, Robert Bonsib, said his client left the group “because he was not comfortable with what they were doing.”

“Nineteen-year-olds are knuckleheads sometimes,” Bonsib told the magistrate. “You’ve got to decide: Is he a knucklehead or a terrorist? And he’s a knucklehead.”

Sullivan, who called it “troubling” that Bilbrough had described himself as a group leader, said it was a “close call” whether to keep the teen detained. The magistrate said he considered Bilbrough’s age, “but anybody can pull the trigger no matter how old they are.”

Mathews’ attorney, Joseph Balter, said his client may have used “alarming” and “outrageous” language in conversations captured on video at a Delaware home in the days leading up to the rally. But Balter said his client’s statements are protected by the First Amendment as free speech and did not reflect any specific plans for violence.