It began around 5:30 in the morning, on the fourth floor, with a fight between rival groups of inmates. Witnesses described an improvised flamethrower, fashioned in a cell block, igniting mattresses and the heaps of flammable material that crowded the space. The flames spread fast through the tier. The men inside could not escape it - they were sealed behind closed gates, and those who died were trapped there, unable to reach the air or the exits just beyond the bars. It took local firefighters about three hours to bring the fire fully under control. By then the worst was long over.

The numbers explain much of the horror. San Miguel had been built to hold 892 people. On the night of the fire it held 1,654 - nearly double its capacity, men stacked into shared cells with little ventilation and no real escape route. According to investigators, the disaster was made worse by the response: once the blaze began, guards reportedly waited around eighteen minutes before calling the fire brigade, and prisoners stayed trapped inside while firefighters worked through the prison's security procedures simply to get in. A handful of staff were on duty for more than a thousand and a half inmates. The overcrowding was not an accident of one night. It was the ordinary condition of the place.

It is easy to let a number like eighty-one stand in for the dead, but they were not a statistic. Most were under thirty. Many had not been convicted of anything - they were in pretrial detention, presumed innocent under the law, waiting for a court date that for them never came. Others were finishing short sentences for offenses as small as marijuana possession or, like Arriagada, selling counterfeit goods. They were sons and brothers and fathers, sent to prison for weeks or months and condemned, by overcrowding and locked gates, to a death sentence no court had handed down. The families who came to identify them at the morgue had expected to welcome many of them home within the year.

The fire forced Chile to look at a prison system it had long ignored. President Sebastián Piñera ordered an investigation and spoke with unusual bluntness, calling the system "absolutely inhumane" and pledging to build one "that befits a civilised country." The political will, for a time, was real. Yet justice for the dead proved elusive: years later, a Santiago court cleared the prison guards of manslaughter, and investigations found that conditions across Chile's prisons remained dangerously crowded. The eighty-one men of San Miguel became a reference point in every later argument about how a country treats the people it locks away - their deaths a measure of the distance between the promises made over their ashes and the prisons that still stood.