CALTANISSETTA, Sicily (AP) _ The reputed Mafia ``boss of bosses'' and 36 other defendants went on trial in a fortress-like courtroom today for the 1992 killing of prosecutor Giovanni Falcone.

Scores of police guarded the courtroom and surrounded Salvatore ``Toto'' Riina as he was led into a bulletproof pen holding the defendants.

Riina, arrested two years ago after 24 years in hiding, is accused along with other defendants of masterminding Falcone's slaying.

The top anti-Mafia prosecutor was killed by a bomb planted on a Sicilian highway on May 23, 1992. His wife and three bodyguards also died in the attack.

Falcone was a symbol of Italy's renewed efforts to crack down on the crime syndicate. In the years following his death scores of top mobsters were arrested.

Ten defendants attended today's opening session, including another reputed top boss, Benedetto ``Nitto'' Santapaola.

Helicopters flew overhead as the defendants were driven to the courthouse. Fearing possible bomb attacks, police inspected and sealed manholes along the route.

At the request of one defendant, TV cameras were barred from the courtroom.

The two-hour session was devoted to procedural matters and the trial was adjourned until April 19.

Authorities in Caltanissetta launched an unrelated Mafia sweep today, issuing 54 warrants for 23 mob-related killings in the province over the past seven years. Prosecutors said 12 people were arrested, two were listed as fugitives while the other warrants were issued to people already in prison on other charges.