One of five men arrested last week on suspicion of carrying out an audacious jewellery theft at the Doge’s Palace in Venice in January is on the run again after escaping from police custody in Croatia, according to Italian media.

Dragan Mladenović, a 54-year-old from Serbia, managed to flee after climbing through a bathroom window before Italian police who had travelled to the country were able to question him. Other reports say Serbian police claim he escaped after attacking an agent.

Either way, his escape resembled the techniques used by the thieves who stole €2m-worth (£1.7m) of jewellery owned by a member of Qatar’s royal palace on the final day of the four-month Treasures of the Mughals and the Maharajahs exhibition at the Doge’s Palace. In a case that has perplexed police for 10 months, they managed to deactivate the alarm system, break into a reinforced case and seize earrings and a brooch before escaping into the crowds.

Local police called on experts to help try to establish how they managed to pull off the heist in the Chamber of the Scrutinio, one of the rooms within the vast premises of the palace, which was once the residence of the former republic of Venice’s rulers and attracts up to 4,000 visitors a day.

The mayor of Venice, Luigi Brugnaro, said justice had been delivered “to those who thought they could commit a crime in Venice and get away with it”.

The jewels, which were part of a collection of 270 Indian gems and jewels that was presented in Italy for the first time, are yet to be retrieved.