Three cats have been found strangled to death with their own collars and dumped in bushes in Leeds, the RSPCA said. City council refuse collector Christopher Rothery found the animals on Haslewood Drive, Burmantofts.
Mr Rothery, 51, said the discovery was heartbreaking and "the most horrific thing I have ever seen".
The RSPCA described the killings as a "shocking and deliberate act of cruelty" and urged anyone with information to contact them.
RSPCA inspector Jo Hartley said the cats were believed to have been pets.
She said: "Sadly, companion animals have very trusting natures and can easily be coaxed in to terrible situations like this.
"It's important for animal owners to keep a watchful eye on their pets and report back if they go missing for any length of time."
Mr Rothery added: "I was heartbroken when I saw the cats lying there, and can't imagine the terror they were put through at the hands of these cruel individuals
"They were in a terrible state and I could see the fear in their eyes."