James Mathew Bradley Jr, 60, was charged with one count of "transporting illegal aliens" for his role in the journey that one migrant told investigators was apparently under the protection of the Zetas, a powerful Mexican criminal cartel.
The federal charge against Bradley is punishable by life imprisonment or even theoretically the death penalty, although the US government has not carried out an execution in 14 years.
The migrants were discovered Sunday just after midnight in a truck parked in a Walmart lot in San Antonio, a city that is a two-hour drive from the US-Mexico border, when one of them approached a store employee asking for water.
The employee brought water and then called police, who found 38 people crammed in the trailer with a broken refrigeration system, parked in the baking Texas heat. Another person was found in nearby woods.
Eight were dead at the scene and two others died later at the hospital.
Thirty people were hospitalized -- including two school-age children -- and more than a dozen were in critical condition, suffering from heat stroke and dehydration, authorities said.
The sweltering trailer may have held between 70 to 200 people, with some migrants fleeing in six black SUVs that had been waiting when the truck stopped in the parking lot, according to witness accounts given to authorities and described in a charging complaint filed in federal court.
The document recounted a harrowing journey, with migrants having trouble breathing and some passing out in the trailer.
"People began hitting the trailer walls and making noise to get the driver's attention. The driver never stopped," according to one of the migrants interviewed, identified only as J.M.M-J.
"People had a hole in the trailer wall to provide some ventilation and they started taking turns breathing from the hole."
It was unclear how long the migrants were inside the truck.
J.M.M-J said he was a Mexican national and part of a group of 29 people being smuggled into the United States. He said they joined 70 migrants already in the truck's trailer.
Authorities had not previously released the victims' nationalities or names, pending notification of their families.
According to the migrant's recollection, his smuggler said "people linked to the Zetas" cartel were offering protection for the journey through Mexico to the US border, and that once arriving in the country he was to pay $5,500, the complaint said.
The driver said he did not know he was transporting people until he stopped at the Walmart store to use the restroom and observed "banging and shaking," prosecutors said.
Bradley said he was delivering the trailer from Iowa to Texas on the orders of his boss, and attempted to administer aid when he found the migrants, but did not call 911, according to the complaint.
Homeland Security Secretary John Kelly in a statement called the deaths "senseless" and the result of a human trafficking "network of abuse and death."
"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," Kelly said.
Kelly has been to Mexico twice to discuss immigration, human trafficking and the sprawling cross-border drug trade.
(This story has not been edited by NDTV staff and is auto-generated from a syndicated feed.)