They victims were discovered after a Walmart employee was approached by a man and who asked for water; the same man later lead the authorities to the truck where the bodies were discovered.
Authorities from Homeland Security and Immigration Customs Enforcement are involved in the investigation. In total, police found 38 people in and around the trailer.
Prosecutors said the driver in the 2003 case heard the immigrants begging and screaming for their lives as they were succumbing to the stifling heat inside his truck but refused to free them.
He said there was no air conditioning in the trailer, leaving people "very hot to the touch".
Officers arrived at about 12:30 a.m.to find eight people deceased and dozens of others suffering from heat stroke or dehydration. He later added that emergency workers used triage techniques to help people in what he called a "mass-casualty" event.
It is considered the most deadly human smuggling incident in US history.
The victims included adults and at least two children.
Police apprehended the driver of the truck at the scene.
"We are very fortunate that there weren't 38 people who were locked inside of this vehicle dead", he says.
Authorities used helicopters to rush some of the injured to seven area hospitals, Hood said.
Experts have warned in recent months that tougher immigration policies could make it more hard to stop human trafficking.
"This is not an isolated incident", McManus said, "This happens quite frequently". Police arrived at the scene shortly after midnight Sunday morning, KENS5 reported.
Raids on suspected illegal immigrants have ramped up across the United States in recent months, after President Donald Trump's vow to crack down on those entering the country without authorization or overstaying their visas. "Fortunately we came across this one; fortunately there are people who survived".