Eight people were found dead in a tractor-trailer outside a Walmart store in what police called a horrific human trafficking case, and the driver was arrested.
Thirty other people who were also in the tractor-trailer were transported to the hospital, according to authorities.
Authorities said the driver had been held, but they didn't release the driver's identity.
A person from the truck approached a Walmart employee in a parking lot and asked for water late Saturday night or early Sunday morning, San Antonio police said. The employee gave the person the water and then called police, and when officers arrived they found the eight people dead in the back of the trailer, police Chief William McManus said.
Firefighters had been called to the scene at about 12:30 a.m. Sunday, CBS San Antonio affiliate KENS reports. Two AirLIFE choppers and at least 29 fire units responded to take care of the victims.
U.S. Immigrant and Customs Enforcement agents and San Antonio police were also called to the scene.
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.
He called the case "a horrific tragedy."
The temperature in San Antonio had been in the 90s just before the eight were found dead. Authorities said the truck didn't have a working air conditioning system despite the blistering summer heat. The National Weather Service said the temperature in San Antonio hit 101 degrees just before 5 p.m. Saturday and didn't dip below 90 degrees until after 10 p.m.
The U.S. Department of Homeland Security was involved in the investigation into what happened, according to McManus.