The driver of a tractor-trailer turned deadly transporter for undocumented migrants is due to face criminal charges in a Texas court Monday in what police are calling a human trafficking crime.

Authorities called to the San Antonio Walmart lot Sunday morning where the trailer was parked found eight bodies and 30 undocumented immigrants severely injured from overheating inside. A ninth person later died in hospital, ICE officials said. Thirty-nine people were recovered from the trailer, including one person who was found in a nearby wooded area.

"Checking the video from the store, we found 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," San Antonio Police Chief William McManus said.

"The driver and whoever else we find is involved in this will be facing state and federal charges," he said.

The US Attorney's Office said the driver, James Matthew Bradley Jr., 60, of Clearwater, Florida, was being held in connection with the incident. Prosecutors plan to file a criminal complaint against Bradley in federal court on Monday morning.

"These people were helpless in the hands of their transporters," said Richard L. Durbin Jr., US attorney for the Western District of Texas.