Italian investigators are looking into how a priceless masterpiece by Leonardo da Vinci may have ended up in a bank vault in the Swiss city of Lugano.

For the last 18 months, magistrates from Pesaro, in the Marche region, have been on the trail of Ritratto di Isabella d’Este, a rarely seen portrait believed to have been painted by Leonardo da Vinci.

There are, in fact, at least two versions of this work, with the first version, a sketch, to be found in the Louvre. For centuries, there was no record of any painting based on that original drawing. In August 2013, however, police in Pesaro received a tip-off claiming that a well-known lawyer in Pesaro had been given a mandate to sell a genuine da Vinci, at an asking price of €95 million.

The tip-off also suggested that the painting in question was the lost Isabella d’Este portrait, part of a private collection kept in a Swiss bank by an as yet unnamed Italian family.

The marchesa of Mantua Isabella, wife of Francesco II Gonzaga, was one of the leading patrons of Renaissance artists, sponsoring the genius of artists such as Titian, Raphael, Giovanni Bellini and da Vinci.

Acting on that tip-off, Italian and Swiss police this week finally opened up a bank vault in Lugano to find the painting, which was immediately sequestered by the Italian police.

Checks for authenticity

Although its authenticity will have to be formally checked out on its return to Italy, art experts believe that this may well be the genuine article, partly because da Vinci expert Prof Carlo Pedretti, who has seen the painting, has vouched for its authenticity. Other art experts, however, suggest that the painting could have been done by a contemporary of da Vinci who copied his work.

Tests previously carried out on the painting have shown that the type of pigment in the portrait was the same as that used by da Vinci, while the primer used to treat the canvas seems similar to that employed by da Vinci.

Carbon dating, conducted by a mass spectrometry laboratory at the University of Arizona, has shown that there is a 95 per cent probability that the portrait was painted between 1460 and 1650.

Swiss police believe that the Italian family who held the painting in Lugano had recently tried to sell it to “foreign buyers” at an asking price of €120 million. If that is the case, the family risk being prosecuted for illegally exporting, without a licence, a “work of art”.