(ANSA) - Milan, December 17 - Italy's chief anti-mafia prosecutor blames 'omertà', or a wall of silence, for the relatively small number of organized-crime accusations in northern Italy. "The small number of mafia suspects reported in Lombardy, Liguria, Piedmont and Emilia-Romagna" has much to do with "a wall of silence," said Franco Roberti after speaking before Italy's parliamentary anti-mafia committee on Tuesday. "Those who were victims transform into accomplices, colluding in a perverse relationship that manifests itself in omertà, silence, rather than reporting crimes to the police". Italy's major mafia organizations are all based in the south. In recent years syndicates like the Naples-based Camorra and Calabria-based 'Ndrangheta have made serious inroads in the richer industrial north.