A member of the public made the “shocking discovery” in Waltham Road, Sutton, on Saturday, December 30 – just a day before the start of the ban on the breed.
The dog had its legs bound together, one of its ears cut off, and had been set on fire, the charity said.
The dog’s death has sparked reaction in the community, leading to misleading information circulating on social media, according to police.
They clarified that the dead dog was not the same as another previously owned by a local family, who are now reportedly facing hostility.
The police confirmed the dog’s owner was identified and not banned from animal ownership.
They reiterated their call for people to withhold speculation during the ongoing investigation.
The most recent statement released by Metropolitan Police reads: “It appears that some information circulating the local community and social media is inaccurate, leading to increased tensions and further crimes/incidents.
“For clarity, the identity of the XL Bully Dog found deceased on 30 December 2023 has been confirmed. The owner has been verified and was not subject to a ban from having animals.
“This dog is not the same as one previously owned by a family in the local area who are now being targeted following this incident.
“Nevertheless, the animal cruelty that has been committed is being treated seriously and anyone’s suspected involvement will be investigated.
“Once again, we encourage people not to speculate while enquiries are ongoing and to contact the RSPCA appeals line on 0300 123 8018 with any information.”
The dog was found the day before new laws came into force making it illegal to breed, sell, or abandon XL bullies.
Owners have to apply for an exemption by February 1 to keep their dogs.
The RSPCA opposes the ban, introduced in response to a spate of attacks by XL bullies, and previously warned it could lead to an influx of the dogs being taken to animal shelters or abandoned.
Harriet Daliday, RSPCA inspector, said: “It is deeply concerning that the dog was found with his legs tied together and had been set on fire.
“The dog also had one of his ears cut off.
“We are appealing for anyone who has any information about this incident to contact us in complete confidence.”
The original statement by a Metropolitan Police spokesperson said: “At 10.54am on December 30 2023, police were called to a report of animal cruelty after an XL Bully dog was found deceased in an alleyway near Waltham Road.
“Officers attended, along with the RSPCA, and located the owner, who reported the dog had been missing for two days.
“The owner is not being treated as a suspect with the current evidence we have.
“We are aware that there have been a number of comments on social media and we would encourage people not to speculate while enquiries are ongoing.
“The investigation is being led by the RSPCA and supported by the South Area BCU.
“Anyone with information should contact the RSPCA appeals line on the 0300 123 8018 quoting reference 01202686.”