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SAN ANTONIO — The driver of a semitrailer packed with at least 39 immigrants, 10 of whom died, pleaded guilty Monday to making the deadly smuggling run.

James Matthew Bradley Jr. pleaded guilty in federal court in San Antonio to a conspiracy count and a count of transporting the immigrants, resulting in death. He faces as long as life in prison when he's sentenced on Jan. 22.

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Bradley, 61, of Clearwater, Florida, could have faced the death penalty had he gone to trial.

Authorities say at least 39 immigrants, most of them Mexicans, were packed into the sweltering trailer, which San Antonio police found in July in a Walmart parking lot. Court records indicate that surviving immigrants estimated that at least 70 and as many as 200 people were carried in the trailer during the trip.

The truck's refrigeration system wasn't working, and investigators say passengers had difficulty breathing as temperatures climbed to 101 degrees in San Antonio that day.

Related: San Antonio Tragedy Puts a Spotlight on Smuggling-by-Truck Cases

A co-defendant, Pedro Silva Segura, 47, of Laredo, Texas, faces two conspiracy counts, including one of conspiracy to transport and harbor undocumented immigrants for financial gain, resulting in death. Segura is also charged with two counts of transporting undocumented immigrants resulting in serious bodily injury and placing lives in jeopardy. He remains in custody in Laredo without bond awaiting transfer to San Antonio. No trial date has been set.

"Today's admission of guilt by Mr. Bradley helps to close the door on one of the conspirators responsible for causing the tragic loss of life and wreaking havoc on those who survived this horrific incident," said Shane Folden, special agent in charge of Homeland Security Investigations in San Antonio.

Bradley initially denied knowing that anyone was inside the trailer, telling investigators that it had been sold and that he was transporting it for his boss from Iowa to Brownsville, Texas. But he said he had driven to Laredo, and stopped there twice before driving back to San Antonio, in the opposite direction from Brownsville.