The Metropolitan Police says it fears a prolific cat killer, suspected of hundreds of mutilations and killings, could escalate their crimes to attacking vulnerable women and girls.
There have been more than 360 deaths of cats, foxes and rabbits in Greater London since September 2015 and in most cases the animals have had their heads and limbs removed, before the body parts are returned to their owners or the local area.
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.
So far there have been no arrests, although the lead detective has told Sky News that out of 30 to 40 names they are focusing on two or three suspects.
Although there is no direct evidence of a risk to human life, Detective Sergeant Andy Collin says the fear is the killing could escalate.
"There is a known link between serial killers and harming animals when you look into their dark history," he said.
"If you look at offending patterns, the assumption is this killer is getting some form of gratification. The concern is they will cease getting that gratification and escalate the attacks to humans, specifically vulnerable women and girls."
The number of animal mutilations and deaths is on the rise.
In 2015 when the investigation began there were eight recorded deaths.
Last year that number was 114, including the first locations outside of the M25. So far this year 246 animals have been targeted.
Sky News was granted access to join Tony Jenkins, who co-runs SNARL with his partner, on call.
Mr Jenkins told us they get a new report about an animal killing on a near-daily basis.
"For two years now it has completely taken over my life. I can't make plans because I wake up in the morning, feed the animals, the phone goes and I'm jumping in the car and off to God knows where."
While filming with SNARL, a fresh call comes in from Liz, who works at a vets in Wigan: "It was what we thought was a cat but the RSPCA officer said it could possibly be small dog. It was found in a plastic bag near our back gate yesterday morning.
"They'd taken off the legs and the head... sorry, I feel really sick just saying it... they'd taken off the legs and the head, there's no other way of identifying it from our point of view."
Calls like this come into SNARL frequently.
"It's having a devastating effect and ripping people's lives apart," Mr Jenkins said.
"It's widespread, it's very frequent. Now because of the awareness we're getting many more cases reported to us."
There have been two sightings of a possible suspect and a description was issued of a white man in his 40s with short brown hair and possible facial scarring.
But it's not known whether it's one person behind the killings or a gang.
"Obviously a psychopath and they've obviously got sociopathic tendencies... a very dangerous person," Tony said.
Anne from Surrey lost one of her cats to the killer this summer.
Amber was found in a neighbour's garden. She found out after receiving a call from SNARL.
"I still cry about it on a regular basis. I worry about what he's doing to other cats every night - is he doing it tonight?" said Anne.
"It plays on my mind. I think about what else he could be capable of if it wasn't just cats. We've got CCTV around the house now and are putting in floodlights to light up the gardens. I don't feel safe.
"I could go to prison for him. I hate him that much. I'll never forgive him. Ever."
Animal charities PETA and Outpaced are offering a combined reward of £10,000 for any information which leads to the arrest and conviction of whoever is responsible for the killings.
Forensic experts at ArroGen Veterinary Forensics in Surrey are helping examine some of the corpses in the hope of finding fresh evidence.