"It's awful heartbreaking," Monninger said. "This has got me really upset."
Monninger, who owns D&B Produce and Farm Machinery Inc. on Greensburg Road, said he's called the Washington County SPCA and was told they couldn't do anything about the situation. He also called the Maryland State Police, who referred him to the Maryland Department of the Environment.
"There are people out here killing animals one right after another and they don't do nothing," Monninger said.
He said he's tired of waiting for someone to help him.
He's offering a $1,000 reward for information about who or what is poisoning his cats.
Washington County SPCA Executive Director Shelly Moore said Monninger, not someone else, would be at fault if his cats are leaving his property.
"If he's allowing these animals to run at large, he's violating the law. It's really the pet owner's responsibility to make sure their animals aren't exposed," she said.
Moore said that although it's not wise to have antifreeze sitting around, it's not illegal. Antifreeze tastes sweet but can be fatal to pets, she said.
"What we can do is to try and educate the community," she said.
In addition to confining their animals, she said pet owners should check under their cars to make sure the vehicles aren't leaking antifreeze. A pet-safe antifreeze called Sierra is available, she said.
Animals that die mysteriously should be taken to a veterinarian to determine the cause of death, she said.
Monninger said it costs $400 for a vet to do an autopsy on a pet - a price he says he shouldn't have to pay.
Monninger said his will had designated that $10,000 go to the SPCA but said he's cut the agency out since it hasn't helped him.
"If I suspect you have antifreeze on your property that's killing animals, why shouldn't the law come and check you out?" he said.
"I spent a lot of money on my animals. I'm an animal lover. Whoever is out here doing this is tearing me up," he said.