Forty years ago, one of the most widely known mass killings in recent Latin American history occurred in and around the village of El Mozote in El Salvador. A U.S.-backed Salvadoran army unit attacked civilians, resulting in the deaths of more than 1,000 people, 500 of them children.

After decades of fits and starts, a trial has resumed in El Salvador that is shedding new light on the events of those few days in early December 1981, as well as on how much U.S. officials knew and how they tried to cover up that knowledge.

Victims are still — after decades of denial, stonewalling and obfuscation — seeking justice for their suffering and the deaths of family when members of the U.S.-trained and armed Atlacatl battalion and other similarly equipped Salvadoran soldiers slaughtered the villagers.

The massacre was part of a war between an alliance of the military and an oligarchy that had oppressively ruled for five decades and a collection of guerrilla opposition groups that unified in 1980. The conflict’s official start date is typically marked by the 1980 assassination by a right-wing death squad of Archbishop Óscar Romero, who was canonized a saint in 2018. Romero’s killing was the culmination of a half-century-long class war that pitted an extraordinarily impoverished peasantry against an ostentatiously wealthy landed elite that relied on murderous repression to maintain its stranglehold and squeeze profit out of the workers.

Though the United States had been meddling in the region for decades, by the 1960s, both Green Beret and CIA officers were in El Salvador organizing paramilitary groups that would, in the following decades, mature into death squads.

By the height of the Reagan era’s anti-communist fervor, the United States was dumping more than a million dollars a day of military aid into El Salvador. Terrified of any leftist activism in the context of the Cold War, the United States wanted to save face after the prolonged disaster of Vietnam and threw resources into El Salvador — as well as Guatemala and Nicaragua — to try to beat back the alleged Marxist menace. The United States poured in materiel and money. An estimated 75,000 people were killed in the 12-year civil war, half a million were displaced, and tens of thousands went missing. There were dozens of massacres: Whole villages like El Mozote and neighboring hamlets were razed, with survivors left to deal with the tragedy and trauma for decades.