Answer: stray bullet
Tristan, accompanied by his wife, her parents, and their children, is confronted by the O'Banion brothers and police officials; he continued to operate his bootlegging business after they requested that he desist. To frighten him, a police officer fired his gun into the mountains, but tragically, a bullet hit Izzy in the chest and she died instantly. Tristan in turn beats the cop with his own gun until he is practically dead, then carries his wife away from the rest of the family.