"They find out they can't intimidate a horse the way they have intimidated people their whole life," Hardin said. "With both the inmates and horses, the more you push, the more they push back."
The mustangs push back harder.
"I've been kicked, and I've broken probably almost every bone in my hand," Peterson said. "One of my horses flipped over on top of me, snapped my femur. I've had broken ribs, pawed in the face."
But, in this unlikely place, hardened criminals discover they are in possession of something of great natural value: love.
"I love on my horses, and they, you know, after two, three days in the round pen, they're following me around like little puppies," Peterson said.
And in the remarkable journey of mustangs and men, a surprising truth is discovered: Wild hearts can be tamed.
For the full story, watch "Primetime's" "The Outsiders" Tuesday at 10 p.m. ET.