PALATKA, Fla. (AP) — Joseph Moore breathed heavily, his face slick with nervous sweat. He held a cellphone with a photo of a man splayed on the floor; the man appeared dead, his shirt torn apart and his pants wet.

Puffy dark clouds blocked the sun as Moore greeted another man, who'd pulled up in a metallic blue sedan. They met behind an old fried chicken shack in rural north Florida.

"KIGY, my brother," Moore said. It was shorthand for "Klansman, I greet you."

Birds chirped in a tree overhead and traffic whooshed by on a nearby road, muddling the sound of their voices, which were being recorde...