Who was the first Mafia boss to turn informant ("pentito") and explain the inner workings of the organisation, who told  that Geraci took care of the fugitive Riina while he stayed in Partinico?
Nenè Geraci:  According to the pentito Tommaso Buscetta, Geraci took care of the fugitive Riina while he stayed in Partinico. Tommaso Buscetta: Tommaso Buscetta (] ; 13 July 1928 – 2 April 2000) was an Italian gangster, a member of the Sicilian Mafia, who became the first Mafia boss to turn informant ("pentito") and explain the inner workings of the organisation.
Tommaso Buscetta