WADSWORTH, Ill. (AP) - Two days after a truck packed with 59 Belgian draft horses overturned, Illinois State Police and animal rights activists are trying to learn why the animals were being transported in a double-deck trailer designed to haul cattle and pigs.

The accident killed 15 horses, including nine found dead at the accident scene 40 miles north of Chicago. Six others later died or had to be euthanized, authorities said Monday.

The remaining animals are being cared for at area farms. The North Dakota driver of the truck was cited.

"This tragedy was completely avoidable and inexcusable," Sheriff Mark Curran said in a statement. "It is our hope that some good will come of this incident so that these beautiful animals are better cared for in the future."

Dozens of firefighters and volunteers worked for more than five hours Saturday night to free the horses from the wreckage after the trailer collided with a pickup truck at an intersection on U.S. Highway 41 in Wadsworth.

"Picture a narrow trailer, slippery as snot, a dangerous cavern filled with horses piled on top of each other, some of them kicking dangerously," said Colleen Fisch, the coordinator for horse enthusiasts in Wisconsin who helped with the rescue. "They were all in sections too small for horses."

The horses, most of which appeared to be yearlings, were being transported from Indiana to an auction in Minnesota.

Authorities said they were working to investigate who owned the animals and were not sure what would become of the remaining horses.

Scott Golladay, who helped rescuers extricate the animals, said he could hear the animals kicking and screaming inside the truck as it lay sideways across the highway.

"It was God awful," said Golladay, owner of Scott Golladay Stables in Antioch. "I've been in the horse business for over 35 years and this was, by far, the most horrific thing I have ever seen."

Neither driver suffered serious injuries.

The driver of the semi, 34-year-old James Anderson, of McLeod, N.D., was cited for running a red light and failing to reduce speed to avoid an accident.

Illinois State Police safety inspectors were checking the tractor-trailer for equipment violations and said there might be charges related to how the horses were transported.

Fisch said horse enthusiasts from northern Illinois and southern Wisconsin were mobilizing to try to keep the horses from continuing on their journey, which Fisch suspects would eventually be to a slaughterhouse.