SAN ANTONIO - Four people are facing charges and two face the possibility of the death penalty for responsibility in what is the "deadliest human smuggling incident in history," one Homeland Security agent told CNN.

Homero Zamorano Jr., 45, is the alleged driver of the trailer that carried over 60 people, 53 of whom died from heat exhaustion and dehydration. Public records show Zamorano has a lengthy criminal record dating back to the 1990s, and he is facing a charge of involvement in human smuggling resulting in death.

Christian Martinez, 28, is also in custody. Martinez is facing one count of conspiracy to transport migrants resulting in death.

Two others face weapon-related charges.

If Zamorano and Martinez are convicted, they could face life in prison or be sentenced to the death penalty.