Feared Gang's Chief Rose From Elite Military Ranks

Heriberto Lazcano's life was marked by betrayal: The Zetas drug lord was trained by the Mexican military to fight in its elite special forces, only to turn on them to create the country's most savage criminal group.

Mr. Lazcano, who Mexican officials said died in a firefight with the Navy on Monday, took his training to the heart of Mexico's crime machine, first working closely with the Gulf Cartel as an enforcer, then turning on his...