Federal authorities have charged a fourth man in connection with the deaths of 53 migrants trapped in a sweltering tractor-trailer abandoned in Southwest San Antonio. Law enforcement officials arrested Christian Martinez, 28, in the East Texas town of Palestine and charged him with conspiracy to transport undocumented immigrants resulting in death, according to a statement from the U.S. Attorney’s Office. In the aftermath of the grisly discovery on Monday, authorities had already arrested the truck’s suspected driver, Homero Zamorano, 45, along with Juan Francisco D’Luna-Bilbao and Juan Claudio D’Luna-Mendez, both picked up on weapons charges.