Stefan Ramin, 40, from Germany, was visiting the remote French Polynesian island of Nuku Hiva in the Marquesas with his girlfriend when he disappeared last week.
Human remains - which local police believe to be Mr Ramin's - have been found in a campfire.
His girlfriend Heike Dorsch, 37, said he went on a goat-hunting trip with a local guide called Henri Haiti.
She told Britain's Daily Mail that only the guide returned from the hunting expedition and told her: "There's been an accident. He needs help.''
But before she could rush to her boyfriend's aid, Ms Dorsch said, Haiti chained her to a tree and sexually assaulted her.
After hours of abuse, she managed to escape and alert authorities.
A week later, a squad of 22 police officers found ashes in a valley on the island and among the embers were bones including a jawbone, teeth and melted metal - believed to be fillings.
The authorities believe a human body was hacked to pieces and burned.
The remains will be flown to Paris for DNA analysis to confirm they are Mr Ramin's.
Mr Ramin wrote about his plans on Facebook only hours before his disappearance.
In Germany, one of his friends later wrote of the news of his death: "It is unbelievable, unspeakably horrible but may not all be true.''
Henri Haiti has not been seen since he attacked Ms Dorsch and French Polynesian soldiers have joined local police in the hunt for him.
Mr Ramin and Ms Dorsch set off from Haselau in Schleswig-Holstein, northern Germany, in a catamaran for a round-the-world trip.
According to reports the couple, both economists, wanted to end their journey in New Zealand next year.
After arriving in French Polynesia last month, they planned to spend several months on the island of nearly 3000 people.
It is not known whether Ms Dorsch is still in Nuku Hiva.
- New Zealand Herald
