Authorities in Texas made a gruesome discovery Monday when the bodies of 46 migrants were found in an abandoned truck trailer in a remote area of San Antonio.

Twelve adults and four children were found alive at the scene and were taken to the hospital for heat exhaustion and heat stroke, San Antonio Fire Chief Charles Hood told reporters, noting that the individuals found inside the trailer had no access to water. Temperatures in San Antonio topped 103 degrees Fahrenheit Monday.

“We’re not supposed to open up a truck and see stacks of bodies in there,” Hood said. “None of us come to work imagining that.”

According to San Antonio Police Chief William McManus, authorities were alerted about the truck around 6 p.m. local time by an individual who heard cries for help in the area. McManus said the discovery marked the single deadliest border crossing attempt known to authorities. In 2017, 10 migrants died after being trapped inside a truck parked at a San Antonio Walmart, while 19 migrants were also found dead in a truck in the city in 2003, the Texas Tribune reported.

“This is nothing short of a horrific human tragedy,” said San Antonio Mayor Ron Nirenberg during a news conference Monday, adding that the deceased were “families who were likely trying to find a better life.”

Texas governor Greg Abbott was quick to politicize the tragedy, blaming President Joe Biden and Democrats for the continued influx of migrants entering the United States at the Texas border. “These deaths are on Biden,” he wrote on Twitter. “They are a result of his deadly open border policies. They show the deadly consequences of his refusal to enforce the law.”

Speaking to Reuters, Jack Staton, a former ICE official, said the area is popular with smugglers due to the large amount of truck traffic along Interstate 35. “It was only a matter of time before a tragedy like this was going to happen again,” he told the publication.