Updated

Some of the people found packed in a sweltering 18-wheeler parked outside a San Antonio Walmart included Guatemalans and Mexican nationals, officials with both countries said Sunday, as the first details about the deadly alleged human-trafficking case started to emerge.

Eight men were found dead in the truck and one man died later at the hospital, according to Liz Johnson, a spokeswoman for U.S. Immigration and Customs Enforcement. Some 17 people were considered in "life-threatening" condition, The Associated Press reported. ICE had announced 10 were dead before revising the number to nine.

James Mathew Bradley Jr., 60, from Clearwater, Florida, was taken into custody and is due in court Monday, U.S. Attorney Richard Durbin Jr. said. He did not say whether Bradley was the driver of the truck, although investigators said earlier that the driver was in custody.

“A criminal complaint will be filed in federal court in San
Antonio on Monday morning. It is anticipated that Bradley will have an initial appearance shortly after that time,” reads a statement from the Attorney’s Office.

Mexican nationals were among both the survivors and the dead, Mexican Consul General in San Antonio Reyna Torres said, without giving a specific number.  Torres said the consulate has been in contact with relatives both in Mexico and in the U.S.

Guatemala's foreign ministry, meanwhile, said at least two Guatemalans were on the abandoned rig.

The two male survivors told Guatemalan consulate officials that they crossed the border by foot at Laredo and boarded the tractor-trailer, according to Tekandi Paniagua, communications director for the foreign ministry. The pair told officials their final destination was Houston, Paniagua added.

"This tragedy demonstrates the brutality of the network of which I often speak. These smugglers have no regard for human life and seek only profits," Secretary of Homeland Security John Kelly said Sunday night. Walmart released a brief statement Sunday saying it was doing what it could to help investigators.

walmart san antonio

San Antonio police officers investigate the scene at the Walmart. (AP Photo/Eric Gay)

A total of 39 people had been inside the tractor-trailer, including at least four teenagers, Fox 29 reported. Paramedics rushed as many as 20 people to hospitals in critical condition, with others facing “less critical” injuries.

"We’re looking at human trafficking crime here this evening,” Police Chief William McManus said, adding that it was "a horrific tragedy."

The U.S. Department of Homeland Security is also looking into the incident.

A store employee first alerted police after being approached by someone from the truck who was asking for water late Saturday or early Sunday. The vehicle did not have a working air conditioning system when it was found, authorities said.

"They were very hot to the touch. So these people were in this trailer without any signs of any type of water," San Antonio Fire Chief Charles Hood said in a news conference. "It was a mass casualty situation for us."

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.

According to police, surveillance video from the store showed "a number of vehicles" picking up people who survived the trip that were inside the trailer. Some people bolted into the woods, prompting police to search the area in the morning.

The origin of the truck is still unknown. Investigators gathered evidence from the truck on Sunday, which had an Iowa license plate but no other markings.

Thomas Homan, the U.S. Immigration and Customs Enforcement acting director, said in a statement: "By any standard, the horrific crime uncovered last night ranks as a stark reminder of why human smuggling networks must be pursued, caught and punished."

Click here for more from Fox 29.

Fox News' Jake Gibson and The Associated Press contributed to this report.