DIA chief Nunzio Antonio Ferla said the number of homicides thought to be the work of organized crime groups had declined significantly in the last ten to 15 years.

“But the various mafia groups have shown themselves to be extraordinary adept at fitting it to every region and every social milieu,” Ferla told an end-of-year briefing for the media on where Italy stands in its fight against groups like Sicily's Cosa Nostra, Naples' Camorra and Calabria's 'NDrangheta.

As a result, the DIA's work is now increasingly focused on “checking tender processes, combatting money laundering and the acquisition of assets with funds raised through crime.”

Italian authorities confiscated assets ranging from works of art to luxury palaces worth a total of €2.6 billion ($2.8 billion) in 2015 – around a fifth of which have been definitively declared state property.

Matteo Piantedosi, deputy chief of the National Police, said a particular and successful effort had been made to prevent this year's World Expo in Milan being targeted by mafia groups and that the model used would be applied to similar large events in the future.

“The mafia is killing less but corrupting more,” said Rosy Bindi, a lawmaker who chairs the Italian parliament's anti-mafia commission.

Mafia infiltration of apparently clean businesses has been underlined this year by arrests in northern Italy which have confirmed that the 'NDrangheta, credited with controlling much of the world's cocaine trade, has been putting down roots in the richer regions of the country for three decades.

Police believe they are using legitimate activities in the north to recycle the huge amounts of cash that their illicit drugs business generates.

The last year has also seen Rome shaken by revelations that the city administration had, for years, been infiltrated by a mafia-style network which siphoned off millions of euros destined for public services.

Leading members of the alleged Mafia Capitale network are currently on trial on charges of criminal association.