Police in San Antonio found eight people dead and 20 people in “extremely critical condition or very serious condition” in the back of a tractor-trailer early Sunday.

The truck was parked in a Walmart parking lot. A total of 38 people were found inside, including two school-age children.

San Antonio Police Chief William McManus said a Walmart employee called the police after a person who was in the truck was able to get out and approached the employee for water.

Twenty people in critical or very serious condition were transported to area hospitals, Fire Chief Charles Hood told reporters. Another eight people in a less severe condition were taken to another hospital, he said. He said there was no air conditioning in the trailer, leaving people “very hot to the touch.” They had no water and many were suffering from dehydration and heat stroke.

“The truck was loaded with people,” Hood said.

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Temperatures in San Antonio reached highs of 100 degrees or more on multiple days in the past week.

After reviewing Walmart store video, “There were a number of vehicles that came in and picked up a lot of the folks that were in that trailer that survived the trip,” McManus told reporters. “We’re looking at a human trafficking crime here this evening.”

After people in hospitals are treated, the police chief said they would be investigated by Immigration and Customs Enforcement.

He said some of the people who had been in the truck had left to the nearby woods.

Police have the truck’s driver in custody and authorities don’t know how long the truck was parked in the lot. “The driver and whomever else we find that’s involved in this will be facing state and federal charges,” McManus added.

The Department of Homeland Security is involved in an investigation.

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