This episode proves the tragedy of gun laws that allow ready access to firearms by people with low impulse control. The husband was coming home from a card game; why was he armed? Without quick access to the gun, the police get called, and matters are sorted out without killing anyone.
As to the husband's guilt, it may be manslaughter but it isn't murder. It might be excused either as temporary insanity, or an attempt to apprehend a fleeing felon. Perhaps the prosecutor simply declined to charge the husband because he knows a jury wouldn't convict. This is Texas, where Joe Horn doesn't get charged after killing two men with a shotgun for burglarizing his neighbor's home, even though he was in no danger until he confronted them.