Billy "the Kid" Claiborne was present with the Clantons and Mclaurys when the gun fight began. Billy ran when the fighting started. Billy Claiborne was shot and Killed by Frank Leslie. Claiborne was drunk and making threats against Leslie, so Leslie shot him.
Claiborne was a key witness for the prosecution, but ask yourself how much can a man running away see?I have a big problem with his testimony(from the coroners inquest). He says that he saw Ike,Frank,Billy hold up their hands and Tom reach for his coat labels when Virgil asked for their arms. Claiborne would have been beside Ike on the right, if they were all in a line how could he possibly see what his party was doing? Remember he also said that at the same time he saw Doc and Morgan fire the first shots.