A dead, bloodied dolphin was dumped on the front lawn of a Bremer Bay house on New Year's Day, prompting a police and Department of Environment and Conservation investigation.
The dolphin was found on Friday afternoon under a tree in Susan Street, about 600m from the ocean.
DEC nature protection manager Kevin Morrison said the brightness of the dolphin's blood suggested it was injured before it died.
"The injury to the dolphin's throat appears to resemble a knife cut or possibly a rip of the throat tissue with a gaff," he said.
RSPCA WA spokesman Richard Barry said the incident was disturbing and vowed to “go after” anyone responsible if the investigation found the animal had endured pain, suffering or stress at the hands of a human.
Offenders face penalties of as much as $50,000 if convicted of cruelty under the Animal Welfare Act.
“If there is evidence that a human being has been involved in an act of cruelty to this animal, we stand ready to help the police in any way, shape or form we can,” Mr Barry said.
“It is a very odd place for a serration to be, there’s nothing on the body, it looks like it’s just going through the jaw and straight into potentially the skull or the brain.
“If the animal was killed instantly there is no offence under the Animal Welfare Act but if there is evidence that there has been cruelty, the RSPCA would act in exactly the same way as we would with any other animal.”
Anyone with information is urged to contact Wildlife Watch on 1800 449 453 or DEC’s Albany office on 9842 4500.