When authorities found dozens of migrants dead inside a trucker under the sweltering Texas sun, the driver tried to slip away by pretending to be one of the survivors, according to a Mexican immigration officer, Wednesday. 

The driver and two other men remained in custody as the investigation continued into the incident that left 53 people dead. This case is the nation’s deadliest smuggling episode on the U.S.-Mexico border. 

Since the discovery of the 46 bodies near the auto salvage yards on the edge of San Antonio Monday, two more people died on Wednesday. 

According to the chief of Mexico’s National Immigration Institute, the truck contained 67 people. The dead included 27 from Mexico, 14 from Honduras, 7 from Guatemala, and 2 from El Salvador. 

Officials have potential identifications on 37 victims, while others are awaiting verification from other countries, Bexar County Medical Examiner’s Office said. 

Identifying the dead bodies has been difficult as some were found without identification and documents. Some migrants were from remote villages in Mexico and Central America with no phone service to reach their family members. In addition, fingerprint data has to be shared and matched by the governments involved. 

According to Rep. Henry Cuellar, it is unclear when or where the migrants boarded the truck bound for San Antonio. Still, Homeland Security Investigations believe it was on U.S. soil, near or in Laredo, Texas. 

Authorities confirmed that the truck passed through a Border Patrol checkpoint northeast of Laredo on Interstate 35 on Monday. The vehicle was registered in Alamo, Texas but had fake plates and logos. 

Officials in Mexico also released a surveillance photo of the driver smiling at the checkpoint. 

The investigation also probes why the truck was left next to a railroad track. During the discovery, the driver was caught trying to blend in as one of the migrants. 

Some of the victims transported to hospitals were found suffering from brain damage and internal bleeding, according to Rubén Minutti, the Mexico consul general in San Antonio. 

Authorities reported that the San Antonio temperatures on Monday approached 100 degrees Fahrenheit (38 degrees Celsius), and those hospitalized were dehydrated and hot to the touch. 

Jennifer Vanos, an assistant professor at Arizona State University who studied child deaths in hot vehicles, says that it wouldn’t have taken long for the temperature to become deadly. The tractor-trailer was most likely hot even before the migrants got inside. 

With high humidity, lack of airflow, and jam-packed inside, the victim’s bodies could not have cooled through evaporation and would have dehydrated quickly. 

With very limited information about the victims, families from Mexico and Central America desperately sought news of their loved ones.