The tourism minister grimaced as he read aloud the causes of death in autopsy reports of the growing number of Americans who have died recently while vacationing in the Dominican Republic: Heart attack. Septic shock. Pneumonia. More accustomed to ribbon-cutting ceremonies than to grappling with the uproar over Americans turning up dead in their hotel rooms, the minister, Fernando Javier García, insisted that the authorities had nothing to hide. “There is no mystery whatsoever regarding any of these deaths,” said Mr. García, even as he acknowledged that the F.B.I. was investigating what had happened to a Maryland couple found dead...