Serial killings are gripping the Salt Lake City (search) and Denver (search) areas, but it’s not people who are turning up dead – it’s cats.

At least 40 felines have been mutilated in the Denver metropolitan area in the last year – four of them over the weekend – and the 11th murdered pet in Salt Lake City was discovered Tuesday at a country club.

Many of the pets have been cut in half, beheaded or disemboweled. Some have had their organs removed. Most are left out for their owners to find the next day.

“I was just confused as to why anyone would want to do that to a cat,” said Matt Isbell, assistant grounds superintendent at the Willow Creek Country Club in Salt Lake City, where the front half of a gray tabby was found Tuesday.

Two women golfers discovered the cat about 9 a.m. off the tee box on the third hole.

County Animal Services spokeswoman Temma Martin said the animal’s organs had been removed and the cat appeared to have been cut with a sharp object, but little blood was found at the site. The back half of the cat didn’t turn up.

Animal Services is investigating whether the latest killing is connected to the others. Ten dead and mutilated cats and one dog have been found in the Salt Lake City area; five of the cats’ owners have been located, according to Martin.

Colorado authorities are looking into possible links between the Denver and Salt Lake City killings, but so far no clear connection has surfaced.

The dead animals began turning up in both cities at about the same time last spring, continued into summer and then ended in November. They started up again this June.

Martin rejected the theory of a copycat pet killer, pointing to the limited information on the crimes that’s been released to the public.

Police are concerned that the person or people responsible could start attacking humans next, since many serial murderers (search) begin by killing animals.

Some of the animals have been cut with surgical precision. In several cases the attacker apparently tried to taunt the owner by depositing the cat’s remains later.

Certain investigators believe a teenaged terrorist group could be behind the cat killings, but others think it’s just one person – most likely a middle-class male in his 20s.

Authorities agree that there will likely be more of the feline mutilations.

The Colorado penalty for aggravated cruelty to animals is up to 18 months in jail and a $100,000 fine.

Christy Hughes is one of the cat owners whose 15-year-old feline, Bugsy, fell victim to the killer or killers two weeks ago. Her husband discovered Bugsy’s eviscerated body just outside their front door in Aurora, a Denver suburb. Bugsy lay on the front lawn, with a hole in his side. His body had been drained of blood and his lung had been cut out.

“I blame myself, because had I read (the coverage of the killings), I never would have let my cat outside,” she said Monday. “I’ve had a hard time forgiving myself for that.”

Police are worried because people still seem to be letting their cats roam in spite of the serial killings. Hughes said she is telling her two children and husband not to let their two other kittens out anymore.

“For a week, I couldn’t sleep because I just kept seeing my cat over and over,” she said. “It breaks my heart.”

Fox News’ Catherine Donaldson-Evans, Carol McKinley and The Associated Press contributed to this report.