The discovery that Juan's entire band of outlaws, including all of his sons, have been brutally massacred. And of course John's death.
The execution scene.
Juan begins the story only interested in riches and getting that one big score. Later in the story after the death of his family, he finds himself with a bag of valuables worth a small fortune. They may as well be made from tin for all Juan cares. Sean's silent acknowledgement of the situation is equally heartbreaking.