Sorry.......... he was GUILTY!
Yeah Howard went to talk - maybe, and Gable was a cad a gangster and a predator, but Howard shot him with a gun that he took with him to the gambling den.
That her father was a drunk and she was tasting some rough trade was irrelevant. Had he burst in on the previous scene in the hotel and Gable shot him in a struggle I could maybe accept, but this was semi pre-planned.
Poor ending that.