Cantwell's recordings are sometimes titled "Live from Seg" or "Letters from a Charlottesville Jail" - a take on Martin Luther King Jr.'s famed "Letter from Birmingham Jail," written in 1963 after he was incarcerated for participating in Alabama civil rights protests. In one episode, Cantwell says he was reading books sent by allies to "become a real expert anti-Semite" and describes seeing James Fields Jr., who was housed on the same unit. Fields is accused ramming his car into the crowd of "Unite the Right" counterprotesters, killing 32-year-old Heather Heyer.

In his most recent recording, dated Oct. 26, Cantwell criticizes members of the alt-right who have distanced themselves from white nationalism in the wake of Charlottesville.

"This is a war," he said. "You want to just play the center in a war between ideological extremes, all you're going to be doing is getting shot at by both sides."

Martin Kumer, the Albemarle-Charlottesville jail superintendent, said administrators know about Cantwell's recordings but can't stop them because inmates have a right to freedom of speech. He said Cantwell's calls, except for those to legal counsel, are monitored.