Authorities in Thurston County, Washington, are hunting for an apparent serial cat killer they believe is responsible for killing and mutilating at least a dozen cats in the county since February.

Seven of those cats were found dead in August, according to The New York Times.

On Tuesday, the 12th known mutilated cat was found, its body found with “carving” and “surgical-type mutilations,” Olympia Police Lt. Sam Costello told local news station Q13 Fox. He added that, as with the other cats that have been found, the body was “splayed out” and appears to have been “posed” by someone.

In some cases, cats’ bodies had been sliced all the way open and spines had been removed. In one instance earlier this month, a kitten was found beheaded, according to news station KIRO 7.

“This person is a sick, callous, disgusting psychopath,” Paul DeTray, the man who found the latest dead cat, told KOMO News. “To say the least, a little gut-wrenching to see somebody’s beloved pet torn apart like that.”

While the bodies of at least 12 cats have been found in the county, it’s possible that there are more victims of the cat killer or killers. One grisly scene appeared to have possibly involved body parts from multiple cats, the Times notes.

Officials trying to track down the person responsible have a few clues to go on. One cat, a family pet named Ollie who was strangled to death, appears to have fought back. Investigators are hoping that DNA found on Ollie’s claws could lead to a match.

And near the body of a cat named Tubby, investigators found a surgical glove that had apparently been left behind.

Authorities are warning people in the area to keep their pets inside in the wake of the crimes. Earlier this month, Pasado’s Safe Haven, an anti-cruelty organization and animal sanctuary in Sultan, Washington, put up a $3,000 reward ― half of which was donated by Q13 Fox anchor David Rose ― for information leading to the arrest of the killer. Now, after donations from the public and other animal advocacy groups, the reward is up to $36,000.

So far, there’s no evidence that the cat killer has harmed humans. But law enforcement working on the case worry the person responsible may move on to people. Animal cruelty investigator Erika Johnson told the Times that she’s previously prosecuted people for violent acts against humans that started with perpetrators “just desensitizing themselves” by hurting animals.