Matteo Messina Denaro, a convicted mastermind of some of the Sicilian Mafia’s most heinous slayings, died on Monday in a hospital prison ward, several months after being captured as Italy’s No. 1 fugitive and following decades on the run, Italian prosecutors said.

Reputed by investigators to be one of the Mafia’s most powerful bosses, Messina Denaro, 61, had been living while a fugitive in western Sicily, his stronghold, during much of his 30 years of eluding law enforcement thanks to the help of complicit townspeople. His need for colon cancer treatment led to his capture on Jan. 16.

Investigators were on his trail for years and had discovered evidence that he was receiving outpatient chemotherapy at a Palermo clinic under an alias. Digging into Italy’s national health system database, they tracked him down and took him into custody when he showed up for a treatment appointment.