Why are the men hunting down Lupito by the river?

One Saturday night, the peace is interrupted by Chavez, who runs to the house and urges Antonio’s father to accompany him to the bridge. The sheriff, his brother, Chavez exclaims, has been murdered by Lupito, a townsman who has been suffering from the war sickness since his time fighting in World War II. All of the men of the town are assembling at the bridge in order to hunt down Lupito and ensure that he does not kill anyone else.