One day earlier this month, Johny Serna was brought by his mother to pray the rosary at a parish shrine to Santo Toribio Romo, the patron saint of migrants, with his uncle and his best friend. They had a long journey ahead.

The next morning, the trio departed for the US-Mexico border, where they crossed the Rio Grande, finally climbing into a crowded 18-wheeler that would take them part of the way to their ultimate destination, Chicago.

The truck turned out to be a death trap.

Serna, 18, survived the scorching heat and asphyxiating conditions – as did his uncle. But 10 others died in a tragedy that exposed the perils of crossing the frontier illegally – and the callous indifference of the criminals who transport migrants.

About 30 more victims were hospitalised in San Antonio, where the truck and its grim cargo were discovered in a Walmart parking lot, after a supermarket employee became suspicious and called police when one of the passengers asked him for water. As many as a hundred people from Mexico and Central America had been crammed inside.

At least 11 hailed from the small Mexican state of Aguascalientes, where young men head north to make enough money to better their lot in life back home. It’s a long-established rite of passage for successive generations tired of scratching meagre livings from this region of dry highlands dotted with corn fields, guava groves and prickly pear cacti.

Unlike the migrants fleeing for their lives from Central America and violent corners of Mexico, those leaving Aguascalientes are drawn by the economic opportunities offered by the US.

Serna hated factory work and instead laboured in construction and picked guavas. He had a single goal: buying a house. “He wanted to earn more and live a little better,” said his cousin, Omar Romo Serna, a pudgy 18-year-old with a thin beard.

Aguascalientes, in the geographic heart of Mexico, is considered one of the country’s more prosperous states, but even here, the lure of the US is irresistible to many.

Gabriel Hernández, the city manager in Palo Alto – an hour east of Calvillo and home to seven of the trailer victims – cites pay at home as the problem. He says migrants work long and hard hours in the US but don’t feel “exploited” like they do in Mexico, where shifts in factories are long and pay might amount to $85 (£65) a week.

Many migrants simply dream of buying their own homes. Walking the dusty but tidy streets of the town, Hernández – who spent nearly two decades in the US – points out the larger homes with brick facades mean “American money”. Shabby concrete structures with corrugated metal roofs suggest no access to US funds.

Adrián Lara Vega, 27, laboured as a bricklayer but couldn’t afford to move his family from a single room behind his parents’ home, among the chickens and pigs the Vegas raise to put food on the table. Relatives said he couldn’t find work for the three weeks prior to his departure.

“They didn’t leave here for ambition, to get the latest model car,” said Lara’s aunt, Rosalba Vega. “He wanted to feed his family.” Vega, who was injured in the trailer, was trying to reach Florida, where a cousin and other friends from Palo Alto were waiting.

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Even Donald Trump’s migration crackdown and the rise of anti-migrant attitudes in the US is not enough to dissuade the town’s men from seeking better fortunes north of the border, said Patricia Briones, whose husband, José Rodríguez, perished in the truck. “He didn’t want to go to the United States,” she said. “But the economic situation is so dire here.”

Rodríguez, 38, lived in the US for 20 years, working construction jobs in North Carolina. Briones joined him and they raised five children – all US citizens – until Rodríguez was deported in 2016.

He was determined to return: he never readjusted to life in Palo Alto and couldn’t raise a family of five there.

“It’s sad,” Briones said at her parents’ home as her children, aged seven to 15, played with tops and fidget spinners. “José provided for the family. I don’t work outside the home and have to raise five children.”

Facebook Twitter Pinterest Patricia Briones with her children Maceilyn, Joandy and Roandy Rodriguez. ‘José provided for the family. I don’t work outside the home and have to raise five children.’ Photograph: David Agren/The Guardian

It is 500 miles from Calvillo to Nuevo Laredo, the Mexican city that faces its Texas counterpart, Laredo, across the Rio Grande. According to a statement to US federal agents by a migrant from Aguascalientes who was to pay $5,500 for his trip, 28 people were taken over the river by raft at night in three groups.

He was told that people linked to the feared Zetas drug cartel would charge 11,000 pesos ($616, £473) for protection and 1,500 pesos ($84, £64) for use of the raft. The Zetas started providing security to Cuban migrants crossing Mexico around 2004, then expanded this obligatory protection service to other migrants crossing states they controlled.

The Zetas are responsible for some of Mexico’s most notorious migrant atrocities, including two massacres in 2010 and 2011 in which at least 265 migrants were kidnapped from buses, killed and buried in mass graves in the northern state of Tamaulipas.

However, the Zetas have never been directly involved in people smuggling, according to Rodolfo Casillas, an expert in migrant routes and criminal networks at the Latin American Social Science Institute (Flacso).

“Smuggling migrants is a specialist service – the Zetas don’t have the knowledge, experience or prestige in this business. That doesn’t mean the migrants didn’t have to pay them for security at some point,” he said.

“Criminal gangs don’t start and stop at borders – they operate through networks of accomplices which include transport companies and drivers,” said Erubiel Tirado, a security analyst. But he also said that it was not uncommon for other criminal groups to use the Zetas’ name to generate terror or to distract attention from themselves and confuse the authorities.

Once in Texas, the migrants walked for hours and were picked up the next morning and taken to the trailer, where they assembled with others, all waiting to depart in the evening.

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At about 9pm, a man appeared and handed pieces of coloured tape to the groups to distinguish them for the smugglers who would be collecting them later. Don’t worry, the man said: the truck has refrigeration, the trip will be fine.

But the cooling system was broken, and the container became an oven in the summer heat. The outdoor temperature reached a high of 38C (100F) and a low of 24C (75F) in San Antonio on 22 July, and the city is a two-and-a-half hour drive from Laredo.

Panic set in quickly, said Jonathan Ryan, executive director of Raices, a San Antonio-based immigrant legal aid organisation that is helping represent some of the survivors. Some cried, screamed and hammered on the walls. Others lost consciousness and hallucinated when they came round, believing they were dead.

The truck was from Iowa and driven by James Bradley, a 60-year-old with roots in Florida and Kentucky and a long criminal record. He is being held without bail and could face the death penalty.

According to the criminal complaint against him, Bradley “knew the trailer refrigeration system didn’t work and that the vent holes were probably clogged up”.

He told the authorities he was taken by surprise when he got out of the truck to urinate, heard banging and shaking in the trailer and was knocked over as people swarmed out when he opened the doors around midnight.

Some scattered into woodland to the west of the parking lot or were picked up by a half-dozen waiting SUVs. Bradley “noticed bodies just lying on the floor like meat”. Eight were dead and two would die later. But he did not call 911.

Migrants who have recovered from dehydration and other heat-related illnesses and are well enough to leave hospital are being detained by federal authorities.

Attorneys and advocates are seeking their release and gearing up to fight the possibility of deportation. “The survivors of this awful event are now being treated like criminals themselves,” Ryan said.

Michael McCrum, an attorney representing 13 people being held as potential witnesses, said: “I think right now the biggest aspect of their condition is they’re traumatised, they’re scared.” He hopes they will be granted visas in return for helping law enforcement with investigations. “I’ve already broached it with the prosecutors but it’s too early to have anything meaningful [decided],” he said.

It is one of the deadliest migrant-smuggling incidents in the US since May 2003, when 19 bodies were found in a milk truck abandoned at a truck stop in the Texas city of Victoria, 120 miles south-east of San Antonio. The first to die was a five-year-old boy who died in his father’s arms. The refrigeration system had been turned off.

Yet the dangers are not enough to end the flow of migrants, who continue to put their money and their lives in the hands of smuggling networks engaged in a form of hide-and-seek with federal officers along an increasingly militarised border.

Later on Sunday, on the same route from Laredo along interstate 35 taken by Bradley’s truck, agents at a Border Patrol checkpoint found 12 migrants from Honduras and Guatemala in a tractor-trailer. They were alive, but the temperature inside was 43C (109F).



The following day, shoppers filled their trolleys as usual in the Walmart, with its brightly lit aisles, vast array of goods and a long line of American flags draped from the ceiling.

In the shade of a tree in the parking lot, near an orange online orders sign bearing an arrow and the instruction “Pickup”, a modest memorial had emerged. Nestled amid candles, crosses, flowers and teddy bears were two bottles of water.