It was the final time she would speak with her boy. As the train approached the Olivos station, two stops east of Periférico, three metal girders supporting the elevated line gave way, authorities said, plunging the last two cars of the train toward busy Tláhuac Avenue some 15 feet below. The two subway cars separated from the rest of the train and dangled in a horrific, V-shaped tableau as metal and concrete debris from the super-structure plummeted to the bustling boulevard. At least 26 people — train passengers and at least one motorist who was crushed on the avenue below — were kill...