In December 1981 soldiers of the Salvadoran Army's select, American-trained Atlacatl Battalion entered the village of El Mozote, where they murdered hundreds of men, women, and children, often by decapitation. Although reports of the massacre -- and photographs of its victims -- appeared in the United States, the Reagan administration quickly dismissed them as propaganda. In the end, El Mozote was forgotten. The war in El Salvador continued, with American funding. When Mark Danner's reconstruction of these events first appeared in The New Yorker, it sent shock waves through the news media and the American foreign-policy establishment. Now Danner has expanded his report into a brilliant book, adding new material as well as the actual sources. He has produced a masterpiece of scrupulous investigative journalism that is also a testament to the forgotten victims of a neglected theater of the cold war.