CROWN POINT, Ind. (AP) — Prosecutors have asked Indiana State Police to investigate the recent deaths of at least eight dogs from heat-related injuries while being transported in the back of an uncooled box truck.

The dead dogs were discovered July 27 in Lake Station while the truck traveled from O’Hare International Airport in Chicago to a training facility in Michigan.

The animal rights group People for Ethical Treatment of Animals had called for a state police investigation, and the Lake County Prosecutor’s Office formally requested one Wednesday.

The dogs that died were among 18 shepherds in the truck.

The driver, whom police have not named, said he was unaware that the air conditioning in the cargo area of the truck had failed until he heard dogs barking. He pulled off Interstate 94 at a convenience store and gas station in Lake Station. When he opened the back, he found several dogs dead and others suffering. Several store employees and passersby stepped in to aid the dogs.

Jennifer Webber, executive director of the Humane Society of Hobart, responded to the scene and said the dogs displayed signs of heatstroke: salivating heavily, wobbling, vomiting and convulsing.

“There were already several dogs dead on the scene, and multiple failing fast,” Webber said at the time. “Their crates inside the truck were completely trashed on the inside, and the little water bowls were the size you’d give a parrot. And they were empty and torn up as if the dogs were exasperated.”

Webber said she encountered resistance when attempting to gather facts for her investigation. The police officer in charge of the scene told her she could leave because the deaths were an accident that “the owner will take care of.”

The owner, who was driving the vehicle, used abusive language, cursed at her and refused to produce health certificates, Webber said. Such paperwork is typically signed by veterinarians in each state involved and required to move dogs across borders for commerce.

Webber said she doubted a veterinarian would have approved travel that day when heat indices exceeded 100 degrees Fahrenheit (37.8 Celsius).