  In this paper we present the results of the study of Sicilian Mafia
organization by using Social Network Analysis. The study investigates the
network structure of a Mafia organization, describing its evolution and
highlighting its plasticity to interventions targeting membership and its
resilience to disruption caused by police operations. We analyze two different
datasets about Mafia gangs built by examining different digital trails and
judicial documents spanning a period of ten years: the former dataset includes
the phone contacts among suspected individuals, the latter is constituted by
the relationships among individuals actively involved in various criminal
offenses. Our report illustrates the limits of traditional investigation
methods like tapping: criminals high up in the organization hierarchy do not
occupy the most central positions in the criminal network, and oftentimes do
not appear in the reconstructed criminal network at all. However, we also
suggest possible strategies of intervention, as we show that although criminal
networks (i.e., the network encoding mobsters and crime relationships) are
extremely resilient to different kind of attacks, contact networks (i.e., the
network reporting suspects and reciprocated phone calls) are much more
vulnerable and their analysis can yield extremely valuable insights.
