To understand the killing, you have to understand the strange coalition Perón had built. From exile he had blessed both wings of his movement at once: young left-wing Peronists, including the Montoneros and the Peronist Youth, whose icons were closer to Che Guevara than to any general, and a hardened right wing of union bosses, nationalists, and figures like José López Rega, his secretary, who would later found the murderous Triple A death squad. For years Perón had let each side believe he was theirs. As his plane crossed the Atlantic that day, the question both factions had buried for a decade rose to the surface: when the old man finally chose, who would he choose?

The right wing did not wait to find out. The reviewing stand near Puente 12, where the airport access road meets the Camino de Cintura, had been organized by Lieutenant-Colonel Jorge Osinde and other figures of Peronism's hard right. From positions around that platform, armed men opened fire on the columns of left-wing youth gathered below, trapping them in the open. At least thirteen people were identified among the dead, and 365 were wounded; the newspaper Clarín and many witnesses believed the true toll was far higher, but no official investigation ever counted them. Perón's plane was diverted and never landed at Ezeiza. The homecoming he had dreamed of became a name for slaughter.

It is easy, fifty years on, to reduce that day to its factions, its acronyms, its conspiracies, and there were conspiracies enough; even the Italian neo-fascist Stefano Delle Chiaie was reportedly present, threads later pulled by investigators including the Spanish judge Baltasar Garzón. But the dead were not abstractions. They were Argentines who had ridden buses for hours and slept by the roadside, who believed that a better country was arriving on an airplane. Most were young. Some were carried away by strangers as they bled. A photograph survives of one fallen victim being lifted from the ground, and in it the whole euphoria of the morning collapses into a single human weight in other people's arms.

Historians treat the Ezeiza massacre as a hinge in Argentine history. If the great Peronist rally of October 1945 marked the movement's birth, one historian wrote, then 20 June 1973 marked the arrival of its violent right wing as a force that would shape everything after. Within months the left was driven out of the government, López Rega's Triple A was hunting opponents, and the country was sliding toward the 1976 coup and the years of state terror that followed. The killing at Ezeiza was not the Dirty War, but it was a rehearsal for its logic: that fellow citizens could be marked as enemies and cut down, and that no one would be made to answer.