Italian police have found a 500-year-old copy of Leonardo da Vinci's Salvator Mundi in a Naples flat and returned it to a church that had no idea it had been stolen.

Officers said late Monday they had arrested the 36-year-old owner of the apartment on suspicion of receiving stolen goods, after the painting was found in his bedroom cupboard.

Depicting Jesus Christ with his hand raised in a blessing and holding a crystal orb, the painting is part of the Doma Museum collection within the San Domenico Maggiore church complex in Naples.

It is a copy of Leonardo's famous work that in 2017 became the most expensive painting ever sold, fetching $450 million at a Christie's auction.

But the collection has been without visitors for months due to coronavirus restrictions and nobody had reported it missing.

It was not immediately clear how the police came to discover the theft of the painting, but they said it was a "particularly complex operation".

"The painting was found on Saturday thanks to a brilliant and diligent police operation," said Naples prosecutor Giovanni Melillo.

"There was no complaint on the matter and in fact we contacted the (church) prior, who was not aware of its disappearance, as the room where the painting is kept has not been open for three months."

The oil painting is believed to be by artist Giacomo Alibrandi and dates to the early 1500s.

Commissioned theft 

Having returned the painting to the church, police are now investigating how it was stolen in the first place, as there was no sign of a break-in, Melillo said.

"Whoever took the painting wanted it, and it is plausible that it was a commissioned theft by an organisation working in the international art trade," he added.

Video images released by police showed an empty wall inside a large niche where the artwork had been housed, in an alcove behind heavy wooden doors locked with a key.

The arrested man reportedly said he had bought the painting from a flea market. 

San Domenico Maggiore, which has been the victim of thefts in the past, houses many important artworks. Some, including paintings by Caravaggio, Raphael and Titian, have been moved to museums in Naples.   

A file photograph of ‘Salvador Mundi’ and visitors taken on October 22, 2019 during the opening of the exhibition ‘Leonardo da Vinci’ at The Louvre Museum in Paris. Photo: Francois Guillot/AFP

Leonardo's original Salvator Mundi and its copy were shown together in Naples in 2015 during an exhibit organised for a visit by Pope Francis to the city.

Two years later, the painting attributed to da Vinci was bought at auction for a record $450 million by an unknown buyer, making it the most expensive work ever sold at auction. 

Christie's auction house later said that Abu Dhabi's department of culture had acquired the work and it would be shown at the Louvre Abu Dhabi. 

The painting has never been seen in public since and its current whereabouts are unknown.