SAN ANTONIO (AP) -- Authorities called to a Walmart parking lot in San Antonio overnight found eight people dead and 20 others in dire condition in the back of a sweltering tractor-trailer, in what police are calling a horrific case of immigrant smuggling.
The truck's driver was arrested and all 28 survivors were taken to hospitals, where 20 were in extremely critical or serious condition, authorities said. Eight others were being treated for lesser injuries, including heat stroke and dehydration. Their nationalities weren't yet known.
Temperatures in San Antonio reached 101 degrees (38 Celsius) on Saturday and didn't dip below 90 degrees (32 C) until after 10 p.m., according to the National Weather Service. The truck's trailer also didn't have a working air conditioner system, San Antonio Fire Chief Charles Hood said in a news briefing.
"They were very hot to the touch. So these people were in this trailer without any signs of any type of water," he said. "It was a mass casualty situation for us."
A person from the truck initially approached a Walmart employee in the parking lot and asked for water late Saturday night or early Sunday morning, police Chief William McManus said. The employee gave the person the water and then called police, who found the dead and desperate inside the truck.
McManus said the driver was arrested, but he didn't release the driver's name.
Investigators checked store surveillance video, which showed vehicles had arrived and picked up other people from the tractor-trailer, police said.
"We're looking at a human trafficking crime this evening," McManus said, adding many of those inside the truck appeared to be adults in their 20s and 30s but that there were also what appears to be two school-age children, as well. He called the case "a horrific tragedy."
Investigators could be seen gathering evidence from the truck on Saturday, hours after those who were inside — living and dead — were taken away. The trailer had an Iowa license plate but no other markings. The truck was parked on the side of the Walmart and the investigation didn't appear to be interfering with commerce, as customers could be seen coming and going from the store.
The U.S. Department of Homeland Security is assisting in the investigation.
Other cases of human trafficking in the United States have led to more deaths. In May 2003, 19 immigrants who were being transported from South Texas to Houston inside a sweltering tractor-trailer died.
Prosecutors said the driver in the 2003 case heard the immigrants begging and screaming for their lives as they were succumbing to the stifling heat inside his truck but refused to free them. The driver was resentenced in 2011 to nearly 34 years in prison after a federal appeals court overturned the multiple life sentences he had received.
In Mexico, smugglers have often crammed migrants bound for the United States into tractor-trailers, sometimes in hidden compartments. Authorities there have made a number of discoveries of large numbers of people being trafficked in such vehicles in dangerous conditions over the years.
Last December, Mexican immigration officials found 110 migrants trapped and suffocating inside a truck after it crashed while speeding in the Gulf coast state of Veracruz. Most of the migrants were from Central America, and 48 of them were minors. Some were injured in the crash, but there were no fatalities.