On the streets of Croydon on Friday morning, the only apparent sign of slaughter was a very dead pigeon, so trodden into the road as to be barely recognisable as animal remains. But for nearly three years, Croydon and the surrounding area of south London has been the hunting ground for an alleged mass killer of cats.

At one point as many as 15 Scotland Yard officers, plus actor Martin Clunes, were on the case of the so-called M25 cat killer, suspected in approximately 500 cases of slaughter and mutilation reported since late 2015. On Thursday afternoon, however, it was announced that the long-running investigation, Operation Takahe, had concludedthat foxes were responsible.

The response – at least from those who have been pushing for justice since the killings were first recorded – ranged from heavy scepticism to anger. The Metropolitan police’s finding that the cats had been killed mostly by cars and then scavenged by opportunistic foxes was described as “a bombshell” in the local News Shopper. “The Met police revealed that the infamous Croydon cat killer does not actually exist,” it reported.

Samantha Glass, whose cat Harley was killed in April, told the News Shopper that the police verdict was “unbelievable” and claimed there was evidence to show that many of the cats had been “mutilated by a clean slice”.

“There have been decapitated heads lying across London,” Glass said. “What happens when the killer drops back the tail to the doorstep? Do foxes have opposing thumbs to hold a mallet so they can bludgeon a cat before using a blade to decapitate it?”

More campaigners heaped scorn on the conclusion on social media, with @ProtectCatsLDN tweeting updates under #CroydonCatKiller.

But the outrage did not seem to extend to George Street, Croydon, where locals struggled to summon more than mild curiosity. Stuart Hicks, from Sutton, out buying a paper at the newsagent, offered up a few theories and recalled a sign advertising a £10,000 reward for information leading to the killer’s capture, but he said the case was not a topic of much discussion. People found it “a bit too morbid”, he said. Plus, there were more important things to worry about, like Brexit.

At the Ladbrokes down the road, Rocco Ascatigno, picking his Lotto numbers, said his wife had asked him for his view on the cat killer. It could have been a fox, he said, or it could have been something else; he did not seem that invested in finding out which. “It’s not pleasant to think about.”

At the nearby George pub, a local who asked to remain anonymous doubted that the killings were being carried out by one person: the area was too large, the rewards too few. “Who’s going to go around here up to Hertfordshire just to kill a cat?”

Though he self-identified as a dog person, he felt strongly that people should not make light of the deaths: “It’s still someone’s pet.” But the cat killer didn’t crop up often in conversation at the George, he said. “It’s all about Brexit over here. As soon as that’s done, we can move on.”

Behind the bar, a young woman said her cat had gone missing a year and a half ago, but she did not seem unduly fazed by the possibility that it could have been a victim. “What can you do? I think it’s sad, but there are more important things going on in Croydon.” Like what? “Like stabbings.”

Dave Phillips, ordering at the bar, overheard. “Someone’s killing cats? The same person?” He went away to Google it. “It’s the first thing that comes up when I search Croydon,” he said, surprised. He wasn’t a local, but his friend James Adams was. Adams’s father had been locking up all six of his cats every night since the first reports – even his least favourite, the 17-year-old one that “can’t walk, can’t see and often walks into things”. He thought that would probably continue despite the police blaming foxes. “Just in case it isn’t, really.”

Experts have widely voiced the view that the supposed cat killings were in fact foxes scavenging roadkill. Among them is John Bryant, an expert in humane fox deterrent in the London area. “I’ve been in hundreds of gardens helping people deter foxes and I’ve found cats’ heads in gardens, tails and bits of legs,” he said. “They scavenge a dead cat from the road or even a dead fox, break it up and the cubs play with it.”

The Croydon cat killer case would not be the first time people had mistaken urban fox behaviour for something more sinister, said Bryant. He recalled a spate of car brake pipes being cut in south London that prompted a police stakeout, with residents fearing there was someone pursuing a vendetta. The culprit was young foxes. “From July the fox cubs are all hooligans, jumping on cars, chasing each other around and they get underneath cars and just bite anything,” Bryant said.

Dawn Scott, a professor of mammal ecology and conservation at the University of Brighton, said foxes were often mistakenly thought to have killed cats they were seen eating but which had in fact been fatally injured by cars. “There are 9 million cats – 20 times more cats than foxes. Cats frequently get killed on roads and foxes are scavengers.”

The urban fox population in London has doubled over the past 30 years, according to studies by Scott. Much of that has been caused by a growth in people feeding wildlife, with foxes also scavenging bird food and scraps left out for hedgehogs or badgers. But Scott said London’s fox density of 12 per square kilometre was far below the peak of 36 per sq km in Bristol in the 1990s. “There’s loads more food than a fox needs so the numbers could be higher, but we think the urban fox population is regulated by disease and perhaps by self-regulation,” she said.

Rather than focus on foxes, Scott said, we should look at the ultimate Croydon cat killer, the car. “People are killing wildlife with cars, that’s the issue,” she said. “Why? Because cats are out at night and cars are going too fast. If I was in the Croydon area I’d be looking at speed limits.”

At the George, Adams said it was certainly possible that at least some of the hundreds of deaths could have been attributed to a fox. “Or else somebody needs to find a hobby.” “Maybe it is their hobby,” said his friend.

Adams echoed the general view that the cat killer was not a go-to topic of conversation. “We don’t really think about it too much these days. You get used to it around Croydon. There’s so much that goes on round here. Lot of stabbings, absolutely.”

But he added: “I’d be upset if it was to happen [to him], yeah. I wouldn’t want to wake up and see a cat’s head on my doorstep. Who would?”