The organisation on Thursday carried out an autopsy on the body, which was discovered attached to a gazebo on the Sunshine Coast hinterland the day before.

Spokesman Michael Beatty said it appeared the koala, which showed signs of head trauma, had been killed when it was hit by a car.

"All of the indications point to that it would have been dead when it was pinned up there," he said, assuaging the worst fears of animal rescuers.

"But it's still pretty disturbing and we would still like to hear from anyone who has any information," he said.

The animal welfare organisation, which has responsibility for prosecuting crimes under the Animal Care and Protection Act, launched an investigation on Thursday after a photo of the dead animal led to an outpouring of anger on social media.

But Mr Beatty said because the animal was dead when it was screwed to the post, it was likely no laws had been broken.

"Legally under the animal care and protection act there's nothing we can do," he said.

RSPCA inspector Sharni Statham said there may be scope for punishment under the nature conservation act, which is administered by the Department of Environment and Science.

An EHS spokeswoman said penalties for interefering with a koala still applied after the animal was dead and could result in a maximum jail time of two years.

She said massive internal injuries suggested the koala had been hit by a car.

The department has been contacted for comment.

Carers from Koala Rescue Queensland were left horrified by the discovery after a woman reported the discovery in Brooloo Park lookout in Brooloo and a council worker confirmed the animal was dead.

Co-founders Ray and Murray Chambers have both called for jail time for the offender.

"Scumbags, lowlifes, just can't comprehend it eh," Murray told ABC Radio Brisbane on Friday.

The RSPCA continues to investigate the incident and has urged anyone with information to call 1300 264 625.