PALERMO, Italy (AFP) - Tens of thousands of Catholic faithful attended a mass on Saturday putting on the path to sainthood a priest shot dead by the mafia 20 years ago, the first victim of organised crime to be declared a martyr.

The open-air service for the Rev Pino Puglisi was held in a stadium on the waterfront of Palermo, the regional capital of Sicily, where he worked in a crime-heavy working-class neighbourhood. His killing shocked the nation, helping turn public opinion in Sicily against the mafia and leading to a clear rejection by the Catholic Church of the pious gestures made by mobsters.

Father Puglisi was shot in the street on his 56th birthday on Sept 15, 1993, as he was returning home in the Brancaccio quarter in Palermo. He was approached by a kill team of four people, and the priest initially thought it was an armed robbery. When he realised who the criminals were, he smiled and told them: "I have been expecting you."

Two of the perpetrators, who were all caught and given life sentences, later turned against the mafia and became key witnesses in trials that put dozens of gangsters behind bars. One of the two is now a devout Catholic, and the second, the trigger man, told investigators he has been haunted by Father Puglisi's smile ever since.

The killing was ordered by the then godfathers of Brancaccio, the Graviano brothers, who are also serving life sentences for the murder.

The Gravianos were reportedly angry that Father Puglisi was turning young people away from a life of crime and was openly critical of their power.

Palermo Archbishop Paolo Romeo presided at the beatification, with dozens of priests and officials, in contrast to when Father Puglisi's pleas for help were ignored by religious and political leaders.

"Mafiosi often say and show they are believers, but they are behind mechanisms of exploitation and injustice, of hatred and bitterness, of violence and death," Archbishop Romeo said in his homily. "Killings by mafiosi reveal their true nature. They reject the God of life and love."

Palermo's Cardinal Emeritus Salvatore De Giorgi said: "Twenty years after his murder, Don Puglisi is speaking again and louder than ever."