The so-called Croydon cat killer is now believed to be responsible for killing and mutilating five cats in the Northampton area after two more deaths emerged.
Police released details of three cat deaths between August and last weekend, but have confirmed two further cases.
The unnamed cats were found in Duston.
Police said the five deaths were now being treated as part of a Metropolitan Police investigation looking into hundreds of killings across England.
The Met and animal charity Snarl (South Norwood Animal Rescue and Liberty) believe more than 400 animals have been killed in the same manner since 2015.
The five Northampton cats were all dismembered in a similar way - with their heads cut off - leading police and the charity to believe they are the work of one person.
The animals were then left for the owners or members of the public to find.
Northampton cat deaths
- 28 August: The body of Rusty was dumped in a bag on the owner's doorstep in Betjeman Court in Northampton
- 6 September: Cat Topsy was left outside the owner's home in the Kingsley area
- 7 October: The mutilated body of a pet cat was found in Duston (name not released)
- 13 November: Dismembered pet cat was discovered in Duston (name not released)
- 18 November: Cat "deliberately mutilated" and left on car roof in Mendip Road, Northampton
Source: Snarl and Northamptonshire Police
The latest cat death has prompted Northamptonshire Police to issue advice to owners, which includes keeping all cats and rabbits indoors at night.
The Met began investigating a series of "gruesome" killings , which initially began in the Croydon area in 2015, after Snarl raised concerns.
The suspect initially became known as the "Croydon cat killer".
Tony Jenkins, co-founder of Snarl, believes the same person has now claimed the lives of hundreds of cats and rabbits across England, and may well travel as part of his or her work.
The Met launched Operation Takahe to investigate the links between animal deaths and in September experts at a new forensic lab in Surrey began re-examining some of the corpses for new evidence.