A fish with markings that resembled a Koranic text has been found by Kenyan officials after vanishing from the fisheries office where it was stored.
The tuna fish, which had provoked intense interest from Muslims, had apparently been stolen by people posing as National Museum officials.
The fish was found at the shop where it had first come to public attention.
The fish was being studied to find out if the Arabic inscription "You are the best provider" was natural or a hoax.
Sceptics say the writing was the work of someone who caught the fish and then threw it back into the sea.
But others say this would be impossible, and local imams are said to have been talking in the mosques about the fish.
The owner of the Takaungu Fish Shop in Mombasa's old town is being questioned by police, who are also seeking another man in connection with the alleged theft.
The shop-keeper said a man had brought the fish to him for preservation.
Over the weekend, people thronged to the shop after the owner noticed the tuna fish's remarkable markings.
It had been caught by fisherman Said Ali at the end of last week at Vanga, a small fishing port on the Kenyan coast, 50km south of Mombasa.
For safekeeping, the 2.5 kg (five pound) fish was moved to the fisheries department.
After being asked by Muslim leaders in Kenya, Kenya's National Museum had offered to take custody of the fish and preserve it for the country's heritage.
The reported theft followed numerous attempts by locals and Muslim scholars to buy the mysterious fish.
An official at the fisheries department in Mombasa said someone had even offered to pay as much as $150.
Under normal circumstances the fish would fetch not more than $6.