Troy Dock and Jason Sprague were being held in a Collin County jail, each on $1 million bonds. The drivers could still face federal charges, officials said. The truck was registered to Boyd Logistics Inc., but Collin County officials told Dallas Morning News that it wasn't clear if they were Boyd employees or contract workers.
Company president Keith Boyd told The El Paso Times the company is "in the process of implementing an immediate and thorough investigation into the circumstances" of the tragedy and "will push with all due speed to determine how this occurred.
Boyd added that the drivers were not authorized to make any unscheduled stop, except for refueling.
More than 40 immigrants are believed to have been in the truck, but only 27 have been accounted for, said Lynn Ligon, spokesman for the Immigration and Naturalization Service. According to several news sources, the passengers said they each had paid between $1,500 and $2,000 for the trip to Dallas.
The truck, which was carrying medical supplies, apparently began its route Friday in Santa Fe before spending the night at a truck stop in El Paso. Officials estimated the temperature in the trailer reached as high as 130 degrees.