Eeight dogs died of heat-related illness after being transported from O’Hare Airport in the back of an uncooled cargo van through northern Indiana, authorities said.

The dogs were among 18 shepherds being taken Thursday night from O’Hare to a training facility in Michigan City, Indiana, police said.

The driver, whom police did not name, said he was unaware the air conditioning in the cargo area failed until he heard dogs barking. He said he then pulled off Interstate 94 at a convenience store and gas station in Lake Station, Indiana, and that, when he opened the back, found several dogs dead and others suffering.

Store employees and passersby stepped in to aid the dogs.

Jennifer Webber, executive director of the Humane Society of Hobart, responded to the call at 7:40 p.m. 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. “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.”

The Lake Station police called the incident a “freak event” and didn’t respond to phone and email messages seeking further comment.

“This was not an act of animal cruelty or neglect but a mechanical failure of the AC unit that was being used in the cargo area,” a written statement from the police said.

But Webber said she encountered resistance when she tried to gather facts for the investigation she is authorized to conduct. She said 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 car, 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 on Thursday, when the heat index topped 100 degrees.

“He shouldn’t have been traveling at all, so, No. 1, that is neglectful,” Webber said.

Then, the police let the owner drive away — this time with the door to the cargo area open — with several dead dogs and others that should have been hospitalized in crates that weren’t secured in the cargo area, she said.

Five of the dogs were transported to veterinary hospitals — in ambulances used for people, not in the specialized humane society vans offered on site.

Webber filed a notice of seizure of the dogs when they’re released. According to Lake Station ordinance, the humane society can confine any dog that is “ill, injured or otherwise in need of care” or “reasonably believed to have been abused or neglected.”

But Webber said the Lake Station police blocked the order, directing the hospitals treating the animals to release them to the owner when they are well again. She said this was the first time in her five years working with Lake Station, that happened.