Houston, June 30 : Four men have been charged after 53 migrants died in a sweltering 18-wheeler in San Antonio, a city in Texas near the US-Mexico border, authorities said. The driver of the tractor-trailer, identified as Homero Zamorano Jr., 45, was charged on Wednesday with human smuggling resulting in death, according to the Department of Justice (DOJ). Local media reported he has a lengthy criminal record dating back to the 1990s, reports Xinhua news agency. Christian Martinez, 28, who was arrested on Tuesday in Palestine, Texas, was charged with one count of conspiracy to transport undocumented migrants resulting in death, the DOJ said. An investigation revealed that communications occurred between Zamorano and Martinez concerning the smuggling event, according to the release. If convicted, Zamorano and Martinez could face up to life in prison or could face the death penalty, CNN reported. On Tuesday, Juan Claudio D'Luna-Mendez and Juan Francisco D'Luna-Bilbao, both Mexican citizens, were charged with possessing firearms while residing in the United States illegally, according to court documents and US authorities. Police arrested them on Monday at an address in San Antonio listed on the tractor-trailer's registration. Craig Larrabee, Homeland Security Investigations San Antonio acting special agent in charge, described the human-smuggling event as "the worst" in the US. The tractor-trailer with a fake plate was carrying 67 migrants when it was found on Monday, Francisco Garduno Yanez, head of Mexico's National Immigration Institute, said at a press conference on Wednesday. There was no sign of water in the refrigerated tractor-trailer and no visible working air conditioning unit, according to San Antonio Fire Chief Charles Hood. Those found alive were hot to the touch and suffering from heat stroke and exhaustion. Temperatures in San Antonio climbed to 38.3 degrees Celsius on Monday, while the heat in the packed trailer was likely way higher than that, according to the US National Weather Service. "It's unspeakable," San Antonio Mayor Ron Nirenberg said on Tuesday. "It's a tragedy beyond explanation." Death is a constant risk for undocumented migrants entering Texas, said a report by The Texas Tribune, noting that in 1987, 2003 and 2017, groups of migrants died of heat and dehydration in the state after being trapped in stifling containers. According to the report, hundreds more die alone or in smaller groups as desperation drives them to take fatal risks. The US Customs and Border Protection said it encountered a record number of 239,416 people along the border in May. /IANS