One afternoon in 1994, during his senior year in college, Fredy Peccerelli sat at an anthropology conference in Atlanta and stared at the man onstage. Peccerelli had seen the renowned bone detective Clyde Snow before, but only in a textbook. Snow, who was in his 60s, leaned forward at the lectern, speaking in his genial Texas drawl about blindfolded skulls and bodies dumped in clandestine graves. He wore his usual attire of an Irish tweed jacket, cowboy boots and a fedora.

In his career as a forensic anthropologist, Snow had traveled much of the world. His work had helped to identify the Nazi war criminal Josef Mengele, victims of the serial killer John Wayne Gacy and members of the Seventh Cavalry Regiment, which fell with George Custer at Little Bighorn. More recently, he had founded a burgeoning movement in Argentina, Chile and Guatemala, training local teams to exhume victims of Latin America’s “dirty wars.” At the conference, Snow charmed Peccerelli and the rest of the room with tales of his adventures in Kurdistan, on horseback, searching for the missing. “He glowed,” Peccerelli told me. “He seemed like a character someone had dreamt up.”

Snow’s colleague Karen Ramey Burns also gave a talk that day. It was about a recent exhumation in Guatemala, the country Peccerelli’s own family fled during the civil war 14 years earlier. The first slide in Burns’s presentation showed the inside of a grave from a military massacre site. Several forensic anthropologists, all trained by Burns and Snow and none of them much older than Peccerelli, were using paintbrushes and chopsticks to whittle away at dirt embedded in eye sockets, skulls and femurs.

It was, Peccerelli would say later, his “struck-by-lightning moment.” He signed up for a class in Guatemala City the following January. For three weeks, Burns and members of the forensic team taught Peccerelli how bones can reveal signs of murder: the mark of a machete, for example, or the slice along a vertebra that indicates a slashed neck. At the end, the team offered him a job for $250 a month. Peccerelli flew back to New York and drove his pickup truck from Brooklyn to Guatemala. He planned to stay for one year.