The prisoners came from different places. Some had been legally detained at Penitentiary Unit No. 7 in Resistencia. Others were transferred from prisons in Misiones Province. On December 12, all of them were brought to the Resistencia police headquarters, where they were tortured and locked in individual cells. During the night, an order arrived -- allegedly to transfer the prisoners to a prison in Formosa. The military loaded them into two vehicles, with a police car as escort, and drove north along National Route 11. They never reached Formosa. At some point near Margarita Belen, the convoy stopped. According to testimony from a police officer who was present, the female prisoners were raped and three of the male prisoners were castrated before the executions took place. The bodies of ten victims were taken to the cemetery in Resistencia and buried in graves that had been dug in advance.

The official military account claimed that guerrillas had attacked the convoy on the road, that at least five prisoners had died in the resulting gunfight, and that the rest had fled. The military version named specific individuals -- including Reynaldo Zapata Sonez -- as having escaped during the supposed shootout. But the prosecution later demonstrated that this narrative was a cover story, consistent with a pattern of fabricated confrontations that the dictatorship used repeatedly across Argentina to disguise extrajudicial killings. The graves had been prepared before the prisoners were even loaded into the vehicles. The regime that carried out the massacre -- the National Reorganization Process, Argentina's military junta -- believed it could operate with impunity. It was ordering similar operations across the country, part of the broader campaign of state terror known as the Dirty War. The Margarita Belen massacre is believed to have been ordered by then-Colonel Cristino Nicolaides, reportedly in retaliation for a Montoneros attack on the 29th Mountain Infantry Regiment in Formosa on October 5, 1975, which killed 14 soldiers.

In 1985, two years after the dictatorship ended, the massacre became one of many cases brought before the Buenos Aires Federal Chamber in the Trial of the Juntas -- a landmark proceeding in which Argentina held its former military rulers accountable for crimes against humanity. The court found that the military's version of events lacked verisimilitude and convicted junta leader Jorge Rafael Videla of homicide. The Federal Chambers of Rosario and Parana handed down the same sentence for Cristino Nicolaides, junta leader Leopoldo Galtieri, and Santa Fe Provincial Police chief Wenceslao Ceniquel. Ricardo Brinzoni, who served as Secretary General of the Chaco military province during the dictatorship and later rose to become Chief of Staff of the Argentine Army from 1999 to 2003, was also accused of responsibility for the massacre.

The town of Margarita Belen is small and quiet, the kind of place most travelers would pass through without stopping. But every December 13, it becomes a site of national remembrance. The massacre has entered the broader memorial landscape of Argentina's Dirty War -- a conflict in which an estimated 30,000 people were disappeared, tortured, or killed by the state. The twenty-two people who died near Margarita Belen were not abstractions or statistics. They were individuals with names, families, and lives that the state decided to end on a stretch of flat road in the Chaco. That Argentina later put the men who ordered their deaths on trial -- and convicted them -- remains one of the most significant acts of transitional justice in Latin American history.