SPRINGFIELD, Ill. (AP) — At least eight dogs died of heat -related injuries after being transported in the back of an uncooled cargo van through northern Indiana Thursday night, authorities said.

The dogs that died were among 18 shepherds traveling from O’Hare International Airport in Chicago to a training facility in Michigan City, Indiana, police said.

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

In a statement posted online, the Lake Station Police Department described the incident as a “freak event.” Telephone and email messages seeking further comment were left with the police station Saturday.

“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,” the statement said.

But Webber said she encountered resistance when attempting to gather facts for the investigation she is authorized to conduct. 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 heat indices exceeded 100 degrees Fahrenheit (37.8 Celsius).

The extreme heat is a worldwide problem, and scientists calculate that July will be the hottest month on record.

“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 who should have been hospitalized in crates that were not secured in the cargo area, she continued.

The truck, crates and dogs are evidence she wanted to inspect.

Even more, 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 may confine any dog who is “ill, injured, or otherwise in need of care” or “reasonably believed to have been abused or neglected.”

But Webber claimed that 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 that in her five years working with Lake Station, that has never happened.