Police in San Antonio found eight people dead and 20 severely injured inside a tractor trailer in a Wal-Mart parking lot early Sunday morning in an incident local officials described as a “horrific” human trafficking tragedy.

Late Saturday night, someone from the 18-wheeler approached a store employee in the parking lot to ask for water, San Antonio Police Chief William McManus said at a news conference. After coming back with water, the employee called police, who found eight dead bodies in the back of the trailer.

At least 38 people were found in and around the truck in the parking lot off Interstate 35 in San Antonio, about 150 miles from the U.S.-Mexico border. Eight were pronounced dead at the scene and are believed to have suffered from heat exposure and asphyxiation, police spokeswoman Romana Lopez said.

Seventeen of the vehicle’s occupants were rushed to hospitals with life-threatening injuries. Another 13 had non-life-threatening injuries. At least two of the occupants were school-age children.

National Weather Service. The truck did not appear to have air conditioning or water on board, said San Antonio Fire Chief Charles Hood.

« It was a mass casualty situation for us,” Chief Hood said. “Each one of them had heart rates over about 130 beats per minute. They were very hot to the touch…. You’re looking at a lot of heat stroke, a lot of dehydration.”

The driver, whose identity has not been revealed, was taken into custody and will face state and federal charges, McManus said.

Immigration and Customs Enforcement Acting Director Thomas Homan said in a statement. “These networks have repeatedly shown a reckless disregard for those they smuggle.”

In fiscal year 2016, Homeland Security Investigations initiated 2,110 human smuggling investigations, which resulted in 1,522 criminal convictions, an Immigration and Customs Enforcement spokesman said.

“So long as I lead ICE, there will be an unwavering commitment to use law enforcement assets to put an end to these practices,” Homan said.

Jarvie is a special correspondent.

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UPDATES:

11:45 a.m.: This story has been updated throughout with Times reporting.

5:50 a.m.: Updated to report 20 people were in critical or serious condition.

4:15 a.m.: This article was updated with background on a 2003 case.

3:55 a.m.: Updated with Saturday’s temperature.

3:25 a.m.: Updated with the driver’s arrest.

This article was first published at 2:50 a.m.