How did Gunnar get the scars on his back?

Gunnar was a fighter when he first came to America. When he said that he wanted to quit, his handler put him in the ring with two other men. In self-defense, Gunnar killed one of the men. The sound of police sirens was heard, and whiskey was spilled and caught on fire. Gunnar was trapped and burned in the fire until he was able to escape.