Police are at a loss as to what happened to a huge diamond, worth SFr10 million ($6.1 million), which went missing on a flight from Zurich to Johannesburg. A report in the Swiss newspaper, "Blick", said the gem had been stolen by professional jewel thieves.
The insurers, Lloyds of London, are offering a reward of SFr500,000 to anyone who can shed light on the stone's whereabouts.
A spokesman for the Zurich cantonal police said it disappeared on January 23, after being flown from Geneva to Zurich's Kloten airport, and then on to Johannesburg.
"Blick" quoted an expert as describing the diamond - a 162.4 carat pink stone - as "unbelievably pure and very rare".
Police declined to identify the owner or the intended recipient of the gem.
Zurich police are cooperating in the investigation, which is being led by South African law enforcement officials.
The stone, weighing 32.5 grammes, was insured by Lloyds of London, which is offering a SFr500,000 reward for information leading to its recovery. "Blick" said Lloyds had also employed a private detective to track down the gem.
The newspaper added that the diamond had been stolen by professional jewel thieves.