SOUTH HOLLAND, Ill. – Cook County Sheriff Tom Dart said the seizure by his officers of 37 fighting dogs Friday in this southern Chicago suburb was the largest such raid in Illinois history.

Dart also said the raid was the fourth largest in U.S. history, in terms of the number of dogs seized.

When sheriff’s police and Cook County Animal Control officers raided the soundproofed barn behind a home here, they also found all the signs of a sophisticated dogfighting operation, Dart said, including treadmills, strength-training equipment, and drugs allegedly used to make the dogs stronger and more aggressive.

“Each and every one of these dogs, it is clear, were fighting dogs,” Dart said. “They were bred to be fighting dogs.”

Investigators also seized a boa constrictor from the home, which reportedly belonged to a 29-year-old man arrested in the raid.

No charges had been filed as of early Saturday, but Dart said he expects the man to be charged with multiple felony counts related to dogfighting and owning dogfighting paraphernalia.

“The individual in custody has previously been convicted of animal-related crimes,” Dart said. “As a matter of fact, this is an individual who was just recently convicted of attending a dog fight in Livingston County by Pontiac, Ill.”

“We were involved in that arrest as well,” Dart said. “That was a large outdoor dogfighting event that went on about a year and a half ago.”

Dart said there was no evidence that any dogfights took place at the South Holland site.

He said the investigation began in May after a neighbor told authorities that fighting dogs were being bred and raised in the home.

The dogs seized in the raid ranged from weeks-old puppies to older dogs, some of whom suffered from physical injuries, the sheriff said.

Dart said most of the dogs will probably have to be euthanized because they’re too violent to adopt out.