Federal authorities have indicted 11 individuals in connection with the deaths of seven migrants found inside a sweltering rail cargo container in Texas.

US Attorney for the Western District of Texas, Justin R. Simmons, announced Friday that six individuals were discovered dead inside the shipping container at a rail yard in Laredo, Texas, on May 13. Another migrant was found left for dead alongside the tracks, having apparently fallen from the container.

"It’s very hard to survive in an un-air-conditioned, sealed container with… the temperature being what it was on that day," Simmons stated. The temperatures on that day ranged between 88 and 92 degrees Fahrenheit (31 to 33 degrees Celsius). The container was stacked atop another, lacked ventilation and a cooling system, and could not be opened from the inside.

The group had boarded a train in the border town of Del Rio, Texas, with San Antonio believed to be their intended destination. According to the indictment, the migrants paid between $1,500 and $10,000 to individuals in Honduras, Mexico, and the United States for transportation into the U.S. interior.

After one individual fell from the container when smugglers opened the door, the smugglers allegedly closed the door and fled, leaving the remaining six inside. The next day, a Union Pacific worker discovered the six bodies in Laredo. One of the victims was able to contact their family as they were succumbing to the heat, Simmons said.

The migrants were from Honduras and Mexico and included a 14-year-old boy. The Webb County medical examiner suspected hyperthermia as the cause of death.

The 11 defendants face two charges: conspiracy to transport aliens resulting in death and aiding and abetting the transportation of aliens resulting in death. Both charges carry a maximum penalty of life in prison.

Officials have arrested one defendant in Del Rio and eight others across central and south Texas. Two defendants, a man and a woman, remain at large. Four of the arrested individuals are U.S. citizens, and two are permanent U.S. residents.

Smuggling operations utilizing trains have been a persistent concern, as trains often pause in Mexico before crossing into the U.S., creating opportunities for smugglers to place people or contraband aboard.