Authorities have taken at least three individuals into custody after 64 migrants were found trapped inside an 18-wheeler in Texas earlier this week.

The grim discovery is said to be the largest fatality related to human smuggling in modern Texas history. One Homeland Security agent called the tragedy the deadliest human smuggling incident in American history.

Authorities were alerted to the semi-truck after a worker in the area was walking along the road and heard a distant cry. After authorities descended on the scene, they uncovered a number of migrants, many of whom had already passed away inside the semi-truck. As of Wednesday, the death toll had risen to 53, with 40 of them being men and 13 being women. According to the Bexar County Public Information Office, some of the victims could be under the age of 18. Many of the migrants have already been identified through fingerprint analysis, but authorities are working to continue identifying the remaining victims.

Authorities continue to investigate the circumstances that resulted in the horrific deaths and have been able to confirm that many of the migrants came from Mexico, Honduras, Guatemala, and a few from El Salvador.

It's not clear how long the truck had been parked on the outskirts of San Antonio on the desolate road during the blazing heat. However, officials recounted during the initial press conference that after the truck doors were open, the migrants inside were hot to the touch. Many of the migrants had succumbed to the heat and passed away due to heat stroke and heat exhaustion.

Law enforcement officers shared with reporters that the driver, Homero Zamorano, 45, was high on meth when he was arrested in the nearby area and had to be taken to the hospital. Authorities detail that Zamorano had been hiding in the nearby bushes and had even tried to pass himself off as one of the victims.

Authorities shared early Thursday that the truck had passed a federal immigration checkpoint inside the United States but that the contents of the truck were not checked, allowing the driver to pass through undetected. Texas Governor Gregg Abbot has called out Biden’s administration, blaming the president for the circumstances that led to the death of the migrants. Following the news of the deaths, Abbot tweeted Monday night, “These deaths are on Biden. They are the result of his deadly open border policies. They show the deadly consequences of his refusal to enforce the law.”

Abbot has vowed to tighten checkpoint security throughout his state, announcing that new checkpoints will be added in order to inspect tractor-trailers. Abbot shared during a press release that the Department of Public Safety “will create and implement a checkpoint strategy beginning immediately where they will begin targeting trucks like the one that was used where these people perished.” The move mimics similar efforts Abbott implemented in April in which checkpoints targeted commercial vehicles. The practice lasted only one week and stopped after Mexican governors had vowed to do a better job securing their borders. Along with costing the state an estimated $4.2 billion, the checkpoints established in April burdened trade in the region.

Along with the arrest of the driver, authorities have also arrested 28-year-old Christian Martinez in connection to the abandoned truck. Authorities targeted Martinez after executing a search warrant on Zamorano’s cellphone. Officials detail that the two men had discussed smuggling the migrants. Both men could face the death penalty according to a press release from the Department of Justice.

Authorities were able to trace the truck’s vehicle registration to an address in San Antonio. At the address, authorities were able to apprehend two other men, Juan Claudio D’Luna-Mendez and Juan Francisco D’Luna-Bilbao. Both men were arrested for being in possession of firearms while living in the U.S. illegally. It’s not yet clear how the two men may have played a part in the human smuggling that resulted in the death of the migrants.

Craig Larrabee, an agent with Homeland Security investigating the incident, shares how the smuggling attempt is a sign of how human smuggling has evolved over the years. "This sheds light on how dangerous human smuggling is,” Larrabee explains. "In the past, smuggling organizations were mom-and-pop. Now, they are organized and tied in with the cartels. So you have a criminal organization that has no regard for the safety of the migrants. They are treated like commodities rather than people."

President Biden has called the horrific incident heartbreaking, adding, "Exploiting vulnerable individuals for profit is shameful, as is political grandstanding around tragedy, and my administration will continue to do everything possible to stop human smugglers and traffickers from taking advantage of people who are seeking to enter the United States between ports of entry."

The grim discovery of the deceased migrants comes during a time when illegal crossings along the border have seen a spike over the past couple of months. In May, nearly 240,000 migrant encounters were made by border patrol agents, roughly one-third higher than the same time last year.

Along with a spike in migrant encounters along the border, there has been a rise in the number of migrants who have died during their journey. At least 650 migrants died last year trying to cross; that number is the highest since 2014. Sweltering heat, dehydration, exposure to the elements, and working with dangerous cartels are all risks migrants face when they try to cross the border.

The horrifying tragedy is unfortunately not unique to the area. In 2013, roughly 100 migrants were found in the back of a semi-truck during the blistering summer heat. As a result,18 migrants ranging in ages from seven to 91 were found deceased. The driver of that semi-truck was facing life in prison and was sentenced to nearly 34 years behind bars.