When Koorana's owners John and Lillian Lever performed an autopsy to try to find the cause of death, they were shocked to discover an orthopaedic plate complete with stainless steel crews.

“It was in amongst numerous stones he used as gastroliths to help grind up food,” Mr Lever said.

“No staff and no pets are missing here so for now it's a mystery.”

The plate no longer has any identification numbers and the farmers are now trying to track down its origins.

“We’re still trying to get in touch with the people who manufactured the plate to find out whether it was used for animals or humans or both,” Ms Lever told Tropic Now.

“It was made in Switzerland.”

Ms Lever said the reptile could have ingested it decades ago.

“The plate is pretty old but we just don’t know how old 'MJ' was because you can’t tell how old they are by the size,” she said.

Once the results are in, they say they'll pass the plate onto police, if necessary.

Koorana Crocodile Farm acquired 'MJ' from the Johnstone River Crocodile Farm in Innisfail, at around the same time the farm was purchased by Louis Vuitton.

However, a spokeswoman at the Innisfail office told Tropic Now she couldn’t shed any light on the mystery.

“I can’t make any comment and I just don’t have those details,” she said.

Mr Lever said 'MJ' had once been a wild crocodile.

The previous two owners of the Innisfail farm regularly captured and took in reptiles that were considered aggressive or deemed as problem crocs.

Mick and Margaret Tabone ran the farm from the 1990s until 12 years ago, however their daughter Madeline told Tropic Now 'MJ' wasn't there during that time.

"There was no croc named that.

"I'm 100 per cent sure," she said.

Tropic Now has been unable to contact the other owner, Mark McFadyen.

Also remaining a puzzle is the separate mystery of how 'MJ' died.

His owners say while they can't find a definitive cause of death, he did have lesions on his lungs, indicating a lung infection.