SAN ANTONIO — The chilling screams of a young woman came from a desolate, debris-strewn urban hinterland between salvage yards and railroad tracks on Quintana Road in the outskirts of San Antonio.

When a man who worked for a nearby paving company, Ricardo Quintero, followed the sounds, he came across a ghastly scene. A trailer had its doors ajar. In and around the trailer were piles of badly burned bodies, many of them lifeless. Others gasped for air. A teenage girl wearing all black pounded the asphalt in desperation and pleaded for help.

“She was hysterical,” Quintero recalled.

Quintero described the scene in court testimony during the first days of a federal trial of two men who are accused of being part of a large smuggling ring. Prosecutors say the ring was responsible for the deaths of 53 migrants — 47 adults and six children — on June 27, 2022, possibly the deadliest migrant smuggling incident in the nation’s history.

Testimony from witnesses, law enforcement and survivors has offered a window into the plight of immigrants who sneak into the country and try to stay undetected, rather than turn themselves in to the authorities and request asylum, the preferred route for much of the Biden administration.

As President Donald Trump cracks down on the asylum system and moves to close the border, he has embraced what he has called the humanitarian side of his aggressive immigration crackdown, stopping human trafficking. The gruesome trial in San Antonio is highlighting the perils of trafficking, while the president’s policies make such treacherous avenues to entry potentially more profitable to smugglers.

The two defendants, Armando Gonzales- Ortega, 54, and Felipe Orduna-Torres, 29, are charged with conspiracy to transport noncitizens resulting in death. They are potentially facing sentences of life in prison. A verdict is expected by early April.

Neither of the men is accused of driving the tractor- trailer, or of being at the scene on Quintana Road.

Prosecutors said they intend to prove in court that many of the smugglers involved in the ring knew that the air-conditioning unit for the trailer was faulty, and that many of the migrants who were locked inside were pounding on the walls and screaming for help before the truck finally came to a stop.

Eric Fuchs, an assistant U.S. attorney, told the jury that both men worked behind the scenes to get 64 migrants, including eight children and a pregnant woman, from stash houses in the border city of Laredo, Texas, to the back of the sweltering 53-foot trailer that would transport them to San Antonio.

Many of the victims, Fuchs added, “had cooked in the back of that trailer,” where the temperature reached 150 degrees, and had died of heat exhaustion or hyperthermia.

“Bodies upon bodies piled on each other, claw marks on the inside of the trailer walls, remnants from people desperately trying to escape, an overpowering smell, a mix of death and seasoning,” Fuchs went on, explaining that smugglers tend to spread cooking spices, coffee and Fabuloso, a cleaning product, inside the trailers to mask human odor and trick authorities.

At least four people, among more than a dozen who have been charged in connection with the incident, have pleaded guilty, including the driver, Homero Zamorano Jr., who tried to run from the scene and was arrested nearby. Others are facing charges in Guatemala.

A lawyer representing the two defendants, Edgardo Rafael Baez, said that investigators had found no direct links between his clients and the people who have pleaded guilty.

Baez said prosecutors were relying on several WhatsApp messages attached to his clients’ names to make their case.

“The fact that they don’t have any fingerprints on any of these trailers, is that a reasonable doubt?” Baez asked the jury. “Because if they were part of this conspiracy, obviously they would have fingerprints all over this vehicle.”

During his testimony, Quintero, the witness who encountered the survivor he described as “a little girl,” broke down in tears on the witness stand when he heard an audio recording of her desperate screams, and saw footage of the dead and dying migrants, some of them with foam on their mouths.

He recalled giving the girl a bottle of water and Gatorade and calling 911.

“There is an 18-wheeler,” he told the operator at the time. “These people are dead. Can you send an ambulance, please?”

Some jurors wept with him.

The incident in 2022 happened during a surge of migrants entering the United States, crippling border towns and overwhelming Democratic cities such as Chicago, Denver and New York.

Fuchs said the organization that Gonzalez-Ortega and Orduna-Torres worked for operated like a corporation, with three distinct layers of responsibilities.

Drivers like Zamorano are considered to be at the bottom.

Next are the coordinators, a role that Gonzalez-Ortega is accused of playing. Coordinators’ duties include taking care of the trailers, recruiting drivers and shadowing the trucks during trips.

At the top are organizers like Orduna-Torres, prosecutors say. They see to it that migrants reach stash houses, decide when to move the human cargo and manage the coordinators who handle the drivers.

Juan Francisco D’Luna- Bilbao, a mechanic for the ring who has pleaded guilty to charges related to his role in the incident, testified at the trial in San Antonio. Speaking in Spanish, he told the court through a translator that part of his role was to spread the smell-masking foodstuffs and cleaning fluid in the bed of the truck to confuse inspectors. He testified that several days before the fateful June 27 trip, he told his supervisors that the trailer’s refrigeration unit was not working properly.

Christian Martinez, who played the role of a middleman and has pleaded guilty, testified that he recruited Zamorano, the driver, for the job, and that Zamorano had told him he stopped at least three times on the deadly day to try to reset the air conditioner.

Martinez said Zamorano later informed him that at least twice, he heard “screaming and banging hard” from inside the locked trailer. Martinez testified that when he passed this information on to a conspirator whom he knew only as Cowboy, he was told, “Tell him don’t stop no more. Ya se hizo. You are there.”

When the truck reached its destination on the desolate road in San Antonio, smugglers opened the trailer doors, saw the carnage inside and fled, Martinez told the jury.