Gems reportedly worth 3 million pounds, or $3.9 million, were mysteriously swiped from the Masterpiece art fair in London last week.
Even with high security, the crime went undetected at the stand of Swiss jeweller Boghossian. Staff discovered the gems were missing early on Wednesday morning.
Detectives are studying CCTV footage for clues. About 44,000 visitors attended the fair at the grounds of Royal Chelsea Hospital from June 29 to July 5.