Billy the Kid killed his first man at 15. He shot him in the gut after the fellow pinned him to the floor and started beating on him. That was in Arizona, a place he had fled to after escaping jail for some petty theft charges in New Mexico. But after killing the man he fled back to New Mexico, and there he remained.
After a few years of petty crime he was scooped up and jailed for stealing John Tunstall's horses. Tunstall didn't press charges but offered him a job. "The only man that ever treated me decent" was how the Kid described him. And when he was murdered by the Murray people the Kid, with many of Tunstall's men, went to war.
The Lincoln County War was brutal and violent and the Kid rose to prominence quickly. He fought in almost every skirmish in the war and survived. Because of this he earned quite a name for himself as a hard fighting cowboy.
Eventually the war winded down and the participants were either killed or rounded up. The Kid amongst them. Many picked up and moved, even those that were paroled. Billy wasn't paroled, he was headed for the noose. But that didn't happen. He broke out of jail and after his escape . . . famously gunning down Bob from the jail house window "Hey Bob" and hit him with both blasts of his shot gun . . . he stole a horse and left town singing for all to hear.
Interestingly, Bill the Kid wouldn't leave New Mexico. He remained. He could have, he had plenty of time and no one on his trail. After all his friends had fled in one direction or the other, he rode off into the desert and remained in New Mexico.
There Pat Garrett found him and ambushed him. Shooting him in the back while he stood in a doorway in a dark room, silhouetted by the moon.
But he never left New Mexico . . . .