A second person has pleaded guilty to conspiracy in the case of a deadly smuggling run that left 10 immigrants dead or dying in a sweltering semitrailer.

Pedro Silva Segura, 47, faces up to life in prison after pleading guilty on Thursday for conspiracy to illegally transport immigrants that resulted in death.

At least 39 immigrants, most of them from Mexico, had been packed inside a semitrailer parked in a Walmart parking lot in San Antonio, Texas in July last year.

Up to 200 people including unaccompanied minors may have been crammed inside but many left before police arrived.

The passengers had breathing difficulties in the 100-degree weather as the trailer's cooling system was broken.

Police officers found 39 immigrants crammed into this truck. Pedro Silva Segura, 47, faces up to life in prison after pleading guilty for conspiracy to illegally transport immigrants

The semitrailer was found in a Walmart parking lot in San Antonio, Texas on July 23, 2017. Eight people were already dead and two people died after they were taken to a nearby hospital

The truck driver, James Matthew Bradley Jr., 61, pleaded guilty in October to single counts of conspiracy and transporting immigrants resulting in death.

He will be sentenced March 26 and also faces up to life in prison.

James Matthew Bradley Jr., 61, was the driver of the truck. He pleaded guilty to conspiracy and transporting immigrants in October

According to court documents, Segura operated a 'stash house' in Laredo, Texas - which runs along the Rio Grande.

Undocumented immigrants were smuggled inside the house until they were transported to other urban areas across the US.

Investigators said Segura delivered five illegal immigrants to a semitrailer driven by Bradley on July 22, 2017.

Bradley then drove that truck towards San Antonio with an estimated 200 men, women and children, including several unaccompanied minors, jammed inside as temperatures were in the 90s.

Police were called to a Walmart parking lot early the next morning where they found 39 people - where eight were already dead - in a truck with no air conditioning.

Officers rushed 20 passengers to the hospital and two more died.

More than a 150 passengers were suspected to have already been picked up by immigrant smugglers.

Segura will be sentenced on June 29 for his involvement in the transportation of illegal immigrants.

An estimated 200 men, women and children were transported in the truck. More than 150 passengers are said to have been picked up by smugglers before police officers arrived