On a hot and dusty December day in 1980, the bodies of four American women-three of them Catholic nuns-were pulled from a hastily dug grave in a field outside San Salvador. They had been murdered two nights before by the US-trained El Salvadoran military. News of the killing shocked the American public and set off a decade of debate over Cold War policy in Latin America. The women themselves became symbols and martyrs, shorn of context and background...