It was a damp and dreary November nearly three years ago, when the London Metropolitan Police decided it was time to act. People kept calling with reports of grisly findings: mutilated cats, some with their heads and tails removed in and around the borough of Croydon.
By February, 2015, the U.K's Independent newspaper reported that the mood had escalated to "mild hysteria ... hypotheses included the suggestion that the increases in cases meant the killer could soon graduate from cats to people on the basis that some of history's most high-profile murderers - ranging from the Boston Strangler to Soham killer Ian Huntley - were cruel to animals before turning to human victims."
More and more cat carcasses kept turning up, eventually numbering in the hundreds. Police intensified their hunt for the killer or killers.
On Thursday, Scotland Yard revealed the conclusion in a near-three-year-long investigation determined the likely culprit to be foxes and other wildlife.
"There is no direct evidence of human involvement," police said. "There were no witnesses, no identifiable patterns and no forensic leads that pointed to human involvement."
The foxes, however, were not so sly.
In at least three instances, the foxes were caught red-handed on security video. A check of the footage revealed the foxes scurrying away, cat parts in their mouths.
In other cases, humans did play a part — or at least, their cars did.
Police said some of the cats were roadkill, before likely falling prey to animal scavengers.
"Wildlife is known to scavenge on road-kill, often removing the heads and tails of dead animals," police said.
Such findings in the past have also lead to unwarranted fears of a roving pet butcher, police said. Twenty years ago, another investigation into a "spate" of cat mutilations also led to the conclusion that it was the work of wildlife.
Despite the gruesome outcome of the apparent interactions, the Humane Society says foxes rarely engage with cats. Average adult cats are about the same size as a fox and are also adept at self-defense, leaving foxes generally loathe to attack. But, the group notes, if people are worried, the best protection is to keep cats indoors.
Stateside, officials believe something more sinister is happening in Thurston County, Wash., where more than a dozen cats have turned up dead since February — the last one discovered last month.
In these cases, authorities say, evidence of a human hand is much clearer. The Washington cats have all been found slit down the stomach before being laid out, reports The New York Times.
The local sheriff's office has expressed concern that "a predator/s is lurking and committing such vile crimes within our Community" in a "disturbing serial crime spree."
"These animals are all being displayed. It's almost like a trophy," Erika Johnson, Thurston County Cruelty Investigator told local news station KIRO-TV. "These animals are always being left in busy, public areas for people to find."
A $53,000 reward leading to the arrest and prosecution of an offender has been posted.
But in the U.K., pet owners should now be able to breathe a bit easier, according to Chief Inspector Stuart Orton with the Hertfordshire Constabulary.
"I hope this conclusion brings comfort to pet owners who have, up until now, been frightened to let their animals out at night," he said.