Colombo police said the 32-year-old man, who was visiting the show from China, allegedly asked owner Suresh de Silva to take the jewel out of its case so he could examine it and then swallowed it, the BBC reported Wednesday.
The owner told police he saw the man and an accomplice attempt to replace the diamond with a forgery.
It was unclear whether the diamond was recovered from the man, who was arrested on an attempted theft charge.
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