Scotland Yard has now linked the grisly mutilation murders of more than 400 animals across Britain to a single perpetrator.
Dubbed the "Croydon Cat Ripper" after the South London suburb where he began piling up corpses in 2015, the killer has not limited himself to cats.
Officers from Operation Takahe now believe the same person — or group of people — is also responsible for the murders of scores of rabbits, foxes and swans countrywide.
The cases appear to share a horrifying modus operandi, which involves decapitating, de-tailing and removing the paws of the unfortunate creature before placing its body in a prominent place.
Police have confirmed that the killer struck again at the weekend in Gravesend, north Kent, where another mutilated cat was found. Now they fear its only a matter of time before the perpetrator sets his sights on bigger prey, such as "vulnerable women and girls".
"We know that there is a link between serial killers and cases of violence against animals," said Detective Sergeant Andy Collin, who is heading Operation Takahe.
"The assumption is that this killer gets some form of satisfaction [by killing cats]. The fear is that he will end up not getting it. Who will he attack then?"
Scotland Yard has been running Operation Takahe for two years, working closely with the RSPCA and South Norwood Animal Rescue Liberty (Snarl, an animal rescue organisation.
Snarl publishes a death tally on its Facebook page with daily updates and tributes to victims.
Snarl cofounder Tony Jenkins claims the killing spree dates back to 2015, when he and his partner picked up on similarities among the details of cat deaths showing up in social media.
They noticed that the headless corpses of an increasing number of felines kept appearing near schools, parks and sometimes under the windows of their owners.
After consulting veterinarians, pet owners and local residents, they pieced together a map and timeline of the killings and were able to trigger the attention of investigators.
"The police believe that a person or a group of people are responsible for the deaths and mutilations," Scotland Yard said at the time, although it didn't want to support the theory of a "serial killer".
But public interest in the case helped to mobilise more resources than those usually allotted to animal crimes, including the offer of a reward, which recently doubled to £10,000 ($19,000) thanks to donations from the People for the Ethical Treatment of Animals (Peta), for any information that could help capture the killer.
Last month, police released the first description of the killer based on a handful of sightings. They say he is a white man in his 40s with short brown hair, dressed in dark clothing and carrying a backpack and a flashlight or headlamp.
He's about 175cm tall and "probably grew up in Croydon", police say.