On January 5 in El Potrero, a small town in the Mexican state of Guerrero, a man named Eusebio García Alvarado was kidnapped by a local criminal syndicate. Kidnappings are fairly common in Guerrero—the state, just south of Mexico City, is one of the poorest in the country and the site of some of the worst violence in the ongoing battle between the drug cartels and Mexican authorities. Guerrero’s largest city, Acapulco, is known to Americans as a tourist hot spot. It’s also currently the second most dangerous city in the world, according to a study released by a...