Matthew Osborne, a 29-year-old British tourist suspected of swallowing a rare pink diamond worth more than £100,000 in Australia, has been X-rayed by police.
The stone was snatched from a jewellery store in the northern city of Cairns last weekend by a man who escaped on a bicycle.
Police arrested Osborne as he attempted to a board a flight to New Zealand from an airport in the southern city of Melbourne.
Senior Sergeant Greg Giles told Australian Broadcasting Corporation that police have yet to recover the cut diamond and suspected the tourist swallowed it but that X-rays were inconclusive.
Osborne will be extradited from Melbourne to Cairns tomorrow charged with theft, The Associated Press said.
The diamond's owner, Keith Bird, said police told him the man had admitted stealing the diamond and swallowed it as he prepared to board the flight to New Zealand.
He said Western Australia state police had the suspect's fingerprints recorded for a traffic offence.
But Mr Bird, owner of the Diamond Gallery in Cairns, doubts the diamond is inside him.
"If he thought he'd got away with it, why would you sit at the Melbourne airport and swallow it, and if you have to go to the loo on a flight to New Zealand? That would be a bit dangerous," Mr Bird said.
"If he's not going to confess where the stone is, he's going to do some serious time," he added.
Mr Bird told the Brisbane Times that he has run the jewellery shop for 36 years and estimates that his chances of seeing the "rare as hen's teeth" diamond again at "better than 50%".
"We had a lady in tears a few days ago because she said she'd always wanted to buy the stone," he told the newspaper. "It's quite notorious now."
He also told reporters that the piece had been on display in the store for nine years.
Despite the 200,000 Australian dollar (£108,000) price tag, the diamond is only 0.31 carat with a diameter of 4.3 millimeters, instead earning its value because of its colour.
Queensland Police said in a statement that the stolen diamond is still outstanding and investigations are continuing.
A Foreign Office spokesman said: "We are aware of reports that a British national was arrested at Melbourne airport on Thursday.
"We have been in contact with the local authorities and offered to provide consular assistance."