In 1909, Petrosino travelled to Palermo as part of a joint criminal investigation between police and immigration officials in the US and Italy. He examined Sicilian police files, trying to establish the real identities and backgrounds of numerous New York criminals and determine which ones were wanted in Italy. He was also gathering evidence against members of the Sicilian Mafia who were wanted for crimes in the US. One of the men he was trying to extradite was Vito Cascio Ferro, who he had driven to New Orleans 6 years earlier. After working in New Orleans, Cascio Ferro returned to Palermo and became Capo di tutti capi (boss of all bosses) in Sicily.

In March, Petrosino received an anonymous message from someone who claimed to have information on Cascio Ferro. The informant asked to meet him in the city centre, under Garibaldi’s statue in the Piazza Marina. When Petrosino arrived on March 12, he was murdered by three gunmen. Rumours suggest that Cascio Ferro personally took part in the shooting, but it seems more likely that the Mafia Don would have left this job to three underlings.

http://www.mobsters.8m.com/petrosino.htm