Intention and complicity in Mafia crime has fueled much debate and legal controversies since 'participation in a Mafia organization' was penalized as such (in 1982, via the RognoniLa Torre Act). The modus operandi of Cosa Nostra members when they come to murder had long stood in the way of any attempt to charge 'coresponsible' individuals. The development of categories and subcategories of Mafia crime such as 'external complicity' ('concorso esterno') and 'favoreggiamento' has enabled to punish different forms of complicity. We will focus here on the "Aiello + 14 Trial" (20062009), where a political leader and a famous doctor were charged with 'participation in a Mafia organization'. This will allow us to examine how magistrates can work toward proving the defendants' deliberate intention to act, and how this proofbuilding process raises complex ethical dilemmas.