Who is Crab Little from Somewhere in the Darkness and what is their importance?

Crab Little is a black man who was sent to prison for a crime he did not commit. Crab is accused of killing a guard during the robbery of an armored truck, but Crab refused to go on that heist because of a tooth ache. One of the robbers pointed a finger at Crab, however, and he could not fight this man's testimony.