Police are investigating a string of gruesome cat killings in south London, amid warnings the so-called "Croydon Cat Ripper" could soon begin carrying out attacks on humans. The remains of at least 32 cats have been found dumped on their owners' doorsteps in Croydon and Norwood over the past two years, with animal welfare workers now urging local pet owners to keep their animals indoors.

The cats are believed to have killed with some sort of blade and were butchered so savagely that investigators initially believed they had been killed by foxes. One recently killed cat was discovered in a hedge near her owners' home in Coulsdon with her head and tail removed and her body so badly mutilated that she had to be identified by microchip.

At least seven of the 32 of the victims were killed in recent months, including two this week alone, according to the Sun. As well as the cats that have died, dozens more are said to have returned home alive but suffering horrific knife injuries. Others have vanished and not been seen again.

Animal welfare workers say panicked Croydon residents have been flooding centres with calls, concerned about the safety of their pets. They urged local cat owners to keep their animals indoors "where possible" as it was now clear that "something sinister" was taking place.

Increasing the alarm still further are expert claims that the so-killed Cat Ripper is clearly revelling in the repeat attacks and "enjoying the cruelty and pain caused during the deaths". They are also said to be displaying the sort of sociopathic, bloodthirsty behaviour typically associated with serial killers before they begin attacking people.

Dr Adam Lynes, a criminology lecturer at Birmingham City University told the newspaper: "Some serial murderers are like addicts. They are hooked on killing and can't get enough." He added: "Unless the person responsible is caught soon, I think it's very likely they will continue to kill more cats – and they could even make the leap to attacking humans."

A spokeswoman for the RSPCA told the BBC: "We will be surveying any evidence we are given to see if there is deliberate cruelty involved here." She added: "Thankfully acts of deliberate violence against dead cats are rare and thorough research has shown that these kind of injuries can be caused by wildlife after death."

The Metropolitan Police confirmed that it had received reports of animals being harmed and was working with Surrey Police to investigate. Surrey Police's Sergeant Ross Spanton added: "I would like to reassure the local community that active enquiries are under way to identify those responsible, and I would urge anyone with any information to contact the police."