On Saturday night, Kathy Harrigan fed and brushed Harley, a deaf tabby cat who she had been taking care of for the past two years.

Leaving him in the heated outdoor cat house that she had built him, she went to bed. The next morning when she woke up, she told Q13 Fox News in Tacoma, Harley wasn't waiting for her by the door as usual.

It didn't take long before the police showed up with bad news. Harley had been found mutilated on a neighbor's lawn, they told her — making the semi-feral 20-year-old tabby's death the seventh in a string of killings in recent months that officials in Thurston County, Washington, believe is the work of a serial cat killer.

In each incident, Erika Johnson, an animal cruelty services investigator for the county, told Q13, the cat has been cut open with a scalpel and had its spine removed. Then its body has been prominently displayed in a public place for people to find.

In addition to Olympia, where Harley's corpse was discovered, mutilated cats have been found in the nearby suburbs of Lacey and Tumwater.

In July, another cat was found cut in half in a public park in Port Angeles, 120 miles from Olympia.

Debbie Drake recognized it as her cat, Tarot.

"He was a friend to not only other cats but dogs as well," she wrote on Facebook. "I like to think he was like the cat sheriff of the west side. He wondered his turf and hung with his posse."

The cuts are too clean for the deaths to be accidental, Johnson told Q13. And, in one case, a surgical glove was found next to the cat's body.

"This is not normal and it's very sick behavior," she said.

Less than 48 hours after Harley was found dead in Olympia, a cat named Olly turned up dead a mile away.

"Olly fought for her life, using her claws to try to get away," Johnson said.

A forensic necropsy revealed that she had been strangled before being cut open and having her spine removed, Q13 reported. Investigators are working to see if any DNA samples can be retrieved from her claws and used to identify the person who killed her.

Residents fear that the suspected killer could be a danger to humans as well.

Patrick and Angie Swan's cat Callie was found mutilated in early July after she went missing.

"I said, 'what caused this? Did it get hit by a car?' They said, 'no.' I said, 'Did an animal like a raccoon or a coyote or anything?' And they said 'no.' Then they said, 'This was done by a human," Patrick Swan said. "My fear is, if you're going to do cats, what's next?"

Residents are being warned to keep their pets indoors. A $3,000 reward for information about the suspected serial killer that leads to an arrest and conviction is being offered by Pasado's Safe Haven, an anti-cruelty organization and animal sanctuary in the town of Sultan, and David Rose, an anchor from Q13 Fox News in Tacoma.

Jen tweeted "There's a .catserial killer in Thurston County WA. I can't stress enough how important it is to keep your .catsindoors! Please retweet & tell everyone in .ThurstonCounty& .WaState. Spread the word. Pray that this sicko is caught! .olympia.portangeles"

There have been several cases of cats being serially mutilated in other cities over the past several years. In 2016, a San Jose man pleaded guilty to 21 felony counts related to the torture and deaths of 20 cats. In January, a London man was arrested for allegedly beheading five cats and leaving their bodies in places for "their owners or members of the public to find," according to the Independent.

The Post's Karin Brulliard reported in 2016 how a handful of counties across the country have been registering animal abusers similar to the way sex offenders are registered. Their names, addresses and photos are published on a county-run websites that are searchable by the public.

In Washington state, the maximum jail sentence for a felony animal offense is five years, if it's someone's first offense, according to the Humane Society of the United States . They may be also ordered to pay a maximum fine of $10,000. In 2015, Gov. Jay Inslee, D-Wash., signed a bill that increased charges for those convicted of killing or stealing pets.