It was 10 P.M. on Saturday, March 3, and Josephine, a furry, ginger-haired Abyssinian whose friskiness had delighted her owners, was now the latest casualty of the Croydon Cat Killer, who, by some estimates, had killed 450 small animals, mostly house cats, but also a few foxes and rabbits. So far, despite a nationwide manhunt, he or she is still at large and has left no forensic evidence or other identifying clues, while miraculously evading the more than four million surveillance cameras that monitor Great Britain.

A woman rushed over from across the street to relate the details of the grim discovery: a divorced dad had driven his two sons home to retrieve some of their belongings while his ex-wife was away for the weekend, only to find a neighbor’s cat, dead, in the driveway. The woman, like most residents of the neighborhood, knew all about the Croydon Cat Killer.

The self-styled pet detectives put the corpse in a body bag and were off. They worked their phones in a frenzy, calling the police to report the killing and the local on-call emergency veterinarian to take the body. Finally, after retrieving the cat’s identification details through the microchip embedded in its fur, they contacted its owner, an 80-year-old retiree. “I’m really sorry to ring you with bad news, but your cat has been found dead,” one of the detectives told him. “Have you heard about the Croydon Cat Killer? Right. We attended the scene. Your babe’s body is going to the vet because the police will probably want to attend. Your cat has become a victim, and your neighbor’s yard is now essentially a crime scene.”

The killings started in 2015 in the London borough of Croydon, then spread across the country—serial killers often begin locally and then, with growing confidence, expand outward. The Croydon killer seemed to have moved in concentric circles around the capital and its M25 highway, reaching as far as Birmingham and Manchester. Pushed by petitions, demonstrations, and lurid headlines, such as JACK THE RIPPURR, New Scotland Yard, the headquarters of the Metropolitan Police force for the greater London area, had assigned 15 officers to the case. The police and the Royal Society for the Prevention of Cruelty to Animals (R.S.P.C.A.), Britain’s oldest and biggest animal charity, established in 1824, had commissioned forensic scientists to perform postmortems on 22 of the victims. It was determined that their deaths were due to blunt-force trauma, followed by mutilation with a sharp object, such as a knife or gardening shears. PETA is offering a $7,000 reward for information leading to the arrest and conviction of the killer. Wanted posters are up across the country, as fresh reports of savage butcherings arise with sickening regularity, and criminal psychologists have issued warnings of a bloodthirsty fiend who enjoys “the cruelty and pain caused during the deaths,” as criminologist Adam Lynes told the British tabloid The Sun.

“People are terrified, and the fear really lies in escalation,” says UK Centre for Animal Law trustee Christina Warner, one of many experts predicting that the killer will eventually move on to humans. “There is a known link between serial killers and harming animals when you look into their dark history,” Andy Collin, the Metropolitan Police detective leading the investigation, told Sky News.

“Anyone who thinks this is a story that only affects people with cats is sorely mistaken,” says Elisa Allen, the director of PETA in the U.K. “A history of animal abuse shows up in the records of some of the world’s most infamous criminals. Mary Bell, who strangled two children to death in Newcastle upon Tyne, while she was still a child, had previously strangled pigeons to death. Thomas Hamilton—perpetrator of the 1996 Dunblane massacre, in which 16 children and one teacher died—had squashed the heads of rabbits beneath car wheels when he was a child. . . . [American serial killer] Jeffrey Dahmer had impaled dogs’ heads, frogs, and cats on sticks. I could go on.”