Eight of the individuals were found dead, with a ninth victim dying later on, and survivors were rushed to nearby hospitals. Authorities described the operation as "an alien smuggling venture gone horribly wrong."
The eight bodies found inside a sweltering truck in a San Antonio Walmart parking lot on Sunday morning were the victims of "ruthless" human traffickers, authorities said. A ninth person died later after being taken to a hospital.
Emergency workers removed the eight bodies and rescued 30 children and adults from the truck, which lacked air conditioning. An additional individual was picked up in a nearby wood, bringing the total number of people recovered by the police to 39.
Many of the individuals found alive were in a critical condition and suffering from heat stroke and exhaustion, San Antonio Fire Chief Charles Hood told media.
The victims' bodies "were very hot to the touch," Hood said.
San Antonio Police Chief William McManus said authorities were alerted to the crime scene by a Walmart employee.
"He was approached by someone from that truck, who was asking for water. [He] came back with water, called the police and we arrived on scene and found eight people dead in the back of that trailer," McManus said in a briefing posted on the San Antonio Police Department's Facebook page.
The driver of the truck was arrested and would be charged, US Attorney for the Western District of Texas Richard L. Durbin said later. Durbin's office identified a detained suspect as 60-year-old James Matthew Bradley Jr. from Florida but did not say whether this was the driver of the vehicle.
Bradley reportedly will appear in court shortly after a federal complaint is filed on Monday morning.
In a statement on his office's website, Durbin's office described the tragic discovery as "an alien smuggling venture gone horribly wrong."
"All were victims of ruthless human smugglers indifferent to the well-being of their fragile cargo," the statement said. "These people were helpless in the hands of their transporters. Imagine their suffering, trapped in a stifling trailer in 100-plus degree (Fahrenheit) heat."
A second statement released later reported the death of a ninth individual. All the victims were adult males.
"Officials will not release the identities or alienage of victims until relatives can be notified," the statement read, adding that anyone with information should call the Immigrations and Customs Enforcement (ICE) hotline.
Police chief McManus described the deaths as a "horrible tragedy" and said other suspects had fled the scene as police officers arrived.
"Checking the video, there were a number of vehicles that came and picked up other people who were in that trailer," McManus said.
The trailer lacked air conditioning and temperatures in the city reached as high as 101 degrees Fahrenheit (38.3 Celcius) on Sunday.
Police said that 20 people were airlifted to seven local hospital, with their states of health ranging from "critical to very critical."
AP later reported that of the 30 people found alive in the back of the 18-wheeler, 17 were considered to be life-threatening condition while 13 were being treated for injuries that were no considered life-threatening.
Homeland Security joins the search
McManus said the Department of Homeland Security had joined the investigation, and that the origin of the truck was unclear.
It was also unclear how many people were picked up alive by the traffickers. Acting ICE Director Thomas Homan said more than 100 people may have been squeezed in the cargo area at one point.
Homan added that the incident highlighted the need to crack down on people smuggling.
"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," Homan said in a statement.
"These networks have repeatedly shown a reckless disregard for those they smuggle, as last night's case demonstrates."
Experts have warned that recent moves under the US President Donald Trump's administration to toughen up on immigration could complicate efforts to prevent human trafficking as individuals seeking to enter the US would resort to more desperate means, including using smugglers to cross borders and not reporting crimes for fear of deportation.
Homan said he was committed for combating human trafficking. "So long as I lead ICE, there will be an unwavering commitment to use law enforcement assets to put an end to these practices," he said.
San Antonio is around 150 miles (240 kilometers) from the border to Mexico, though Homan emphasized that it would be unusual for the truck to have carried the individuals across the border as most would-be immigrants attempt that journey on foot.
cb, aw/tj (Reuters, AFP, AP)