In July 1992, the Sicilian Mafia sent a loud and gruesome message to those who would challenge it when it killed a prosecutor named Paolo Borsellino with a car bomb in Palermo. He was the second prosecutor to meet that fate in two months; in May, another bomb had killed Giovanni Falcone.

The assassinations made news around the world, and the second one made the Mafia a new enemy: Rita Borsellino, Paolo’s younger sister. Before her brother’s death she was a pharmacist. After it, she became a leading crusader against the Mafia’s longstanding, often ruthless grip on life in Sicily, where small businesses were routinely extorted for protection money and killings were commonplace.

Ms. Borsellino was often frustrated over the years as she waged that fight. In 2006 she ran for governor of Sicily and lost to Salvatore Cuffaro, the incumbent, who had been linked to the Mafia and later went to prison. In 2009 at an anti-Mafia march, she told Agence France-Presse, “I am angry and less optimistic than 17 years ago, when my brother was slain.” Mafia influence remains a vexing problem in Sicily and elsewhere in Italy.

Yet Ms. Borsellino, who died on Wednesday in Palermo at 73 after what Italian newspapers said was a long illness, lived to see some successes as well. Among others was that when Salvatore Riina, the head of Sicily’s notorious Cosa Nostra crime syndicate and the man who ordered the murders of the two prosecutors, died last year, he was serving 26 life sentences.