(In this July 23rd story, corrects paras 1 and 2 to show that eight bodies were found in truck, not nine; a ninth man died later at a hospital.)

SAN ANTONIO (Reuters) - At least eight men were found dead on Sunday alongside dozens of people discovered inside a sweltering tractor trailer parked at a Walmart store in San Antonio, Texas, in what authorities called a case of “ruthless” human trafficking.

Thirty people, many in critical condition and suffering from heat stoke and exhaustion, were removed from the trailer, which lacked air conditioning or a water supply, San Antonio Fire Chief Charles Hood said. Temperatures outside the vehicle topped 100 degrees F (37.8 C). A ninth man died later at a hospital.

Another person was found in a wooded area nearby and was also being treated, the U.S. Attorney’s Office for the Western District of Texas said in a statement. All the deceased were adult males, it said.

“All were victims of ruthless human smugglers indifferent to the well-being of their fragile cargo,” San Antonio-based U.S. Attorney Richard Durbin Jr. said.

“These people were helpless in the hands of their transporters. Imagine their suffering, trapped in a stifling trailer in 100-plus degree heat,” he said.

The truck’s driver, named by the U.S. Attorney’s Office as James Mathew Bradley Jr., 60, of Clearwater, Florida, was arrested in connection with the incident, the statement said.

A criminal complaint will be filed in federal court in San Antonio on Monday, and Bradley is expected to have an initial court appearance shortly afterward, the U.S. attorney said.

A multiagency investigation was under way.

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The bodies of the dead, who have not yet been identified by authorities, were discovered after officials were led to the trailer by a man who had approached a Walmart employee and asked for water.

San Antonio is about 150 miles (240 km) north of the border with Mexico.

Mexico’s government said it deplored the deaths and that it had asked the authorities for an exhaustive investigation.

In a statement, it said its consul general in San Antonio was working closely with local and federal authorities, as well as the hospitals, to identify the nationalities of the victims and, if necessary, repatriate their remains to Mexico.

‘HORRIBLE TRAGEDY’

Raids on suspected illegal immigrants have ramped up across the United States in recent months, after President Donald Trump’s vow to crack down on those entering the country without authorization or overstaying their visas.

In Texas alone, federal immigration agents said they arrested 123 illegal immigrants with criminal records in an eight-day operation that ended last week.

The San Antonio deaths come more than a decade after what is considered the worst immigrant smuggling case in U.S. history, when 70 people were found stuffed into an 18-wheeler. Nineteen of them died in the incident in Victoria, Texas, about 100 miles (160 km) southeast of San Antonio, in May 2003.

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San Antonio Police Chief William McManus described the latest fatalities as a “horrible tragedy” and said other suspects had fled the scene as police officers arrived.

“Checking the video, there were a number of vehicles that came and picked up other people who were in that trailer,” McManus said.

Twenty people were airlifted to seven hospitals in conditions ranging from “critical to very critical,” Hood said. Eight others are hospitalized in less serious condition, he said.

McManus said the people in the truck ranged from school-age juveniles to adults in their 20s and 30s.

He said the Department of Homeland Security had joined the investigation, and that the origin of the truck was unclear.

Experts have warned in recent months that tougher immigration policies could make it more difficult to stop human trafficking. Measures to harden international borders encourage would-be migrants to turn to smugglers and fear of deportation deters whistle-blowing, they said.

U.S. Immigration and Customs Enforcement (ICE) officials defended the use of tough methods to fight human smuggling.

“So long as I lead ICE, there will be an unwavering commitment to use law enforcement assets to put an end to these practices,” the agency’s acting director, Thomas Homan, said in a statement.

The Border Patrol has regularly reported finding suspected immigrants inside trucks along the U.S. border with Mexico. Earlier this month, 72 Latin Americans were found in a trailer in Laredo, it said. In June, 44 people were found in the back of tractor trailer in the same Texas city, which lies directly across the Rio Grande from Mexico.

San Antonio has a policy of not inquiring about the immigration status of people who come into contact with city officials or police.

It was among several cities in Texas that filed a federal lawsuit last month to block a state law set to take effect in September that would force them to cooperate closely with immigration agents.

“San Antonio will not turn its back on any man, woman, or child in need,” Mayor Ron Nirenberg said in a statement responding to the truck deaths.