Pope Francis paid tribute to a courageous priest murdered by the Sicilian Mafia as a martyr and urged mobsters on Sunday to abandon their evil ways, particularly the exploitation of people in trafficking rackets such as prostitution.

Francis issued his call to organized crime members to convert their hearts, a day after the beatification of the Rev. Giuseppe “Pino” Puglisi in Palermo. The Vatican honored Puglisi as a martyr in the ceremony, 20 years after he was slain in the city by mobsters for defiantly preaching against the Mafia in a neighborhood where Cosa Nostra held sway.

Francis told a crowd in St. Peter’s Square that the Mafia killed the Rev. Giuseppe Puglisi because he tried to keep youths from being recruited by mobsters.

Beatification is the last formal step before possible sainthood. As part of the process leading to beatification, church officials considered statements that convicted Mafiosi had given to investigators. The mobsters told authorities that Cosa Nostra bosses had ordered Puglisi’s murder because he had dared defy the Mafia by his preaching and work with young people. Mafia bosses were convicted of ordering the slaying and are serving life sentences in prison.

The pope didn’t attend the beatification ceremony, which drew tens of thousands of people to an esplanade near Palermo’s seaside. Instead, he used the traditional Sunday papal appearance to pilgrims, tourists and Romans in St. Peter’s Square to hail Puglisi as a martyr and “an exemplary priest, especially dedicated” to serving young people.

“Educating young people according to the Gospel, he took them away from organized crime, and thus it (the Mafia) tried to defeat him by killing him,” Francis said.

Puglisi was gunned down a few months after Pope John Paul II made a pilgrimage to Sicily and angrily called on mobsters to “convert” their hearts. At the time the island was still shocked by the 1992 bomb blast assassinations by Cosa Nostra, two months apart, of Italy’s top anti-Mafia magistrates.

“I think of the great pain suffered by men, women and even children, exploited by so many mafias,” Francis said. He decried the crime syndicates for “making them do work that makes them slaves, prostitution.”

“Behind this exploitation and slavery are the mafias,” the pope said. Francis, two months into his papacy, has branded human trafficking as one of the most terrible evils plaguing the world.

“They cannot make our brothers slaves,” Francis said. “Let us pray that these Mafiosi and Mafiose convert to God,” the pope said, using the Italian words to indicate both male and female mobsters. Women have increasingly been playing command roles in Italy’s organized crime world as crackdowns see many of the male mobsters jailed for long terms, and have long helped syndicates by hiding fugitives in their homes and with other assistance.

Puglisi worked in one of Palermo’s poorest and roughest neighborhoods, trying to give hope and options to young people, often recruited by Cosa Nostra for drug pushing, numbers running and other jobs in the mob’s illicit activities. Francis has repeatedly said his vision of the Catholic church is a “poor church for the poor,” and encouraged clergy to work with people on society’s margins and avoid having the church turn inward.

Investigators say that along with drug trafficking, human trafficking, including in illegal immigrants to work clandestinely in agriculture or factories, and of young people from abroad for prostitution, has become one of the most profitable industries for organized crime.