In 1876, Sonnino traveled to Sicily with Leopoldo Franchetti to conduct a private investigation into the state of Sicilian society. In 1877, the two men published their research on Sicily in a substantial two-part report for the Italian Parliament. In the first part Sonnino analysed the lives of the island's landless peasants. Leopoldo Franchetti's half of the report, "Political and Administrative Conditions in Sicily", was an analysis of the Mafia in the nineteenth century that is still considered authoritative today. Franchetti would ultimately influence public opinion about the Mafia more than anyone else until Giovanni Falcone over a hundred years later. "Political and Administrative Conditions in Sicily" is the first convincing explanation of how the Mafia came to be.