Carabinieri paramilitary police in Palermo said Gaetano Lo Presti, 52, hanged himself in his cell in a Palermo jail Tuesday evening, hours after he was arrested in the raid. State radio said he used his belt to hang himself. Police said the suicide was under investigation.
Investigators believe Lo Presti allegedly headed a Mafia clan in the city's Porta Nuova district, Palermo police said.
The capture of top fugitives in recent years, some of them after years or decades on the run, has weakened Cosa Nostra. Also threatening Cosa Nostra's psychological and economic hold on much of the Mediterranean island has been a steadily spreading rebellion of Sicilian businessmen against paying "protection money" to Mafia henchmen.
Authorities say they ordered Tuesday's raids to head off a bloody power struggle among rival mob bosses to rebuild the crime syndicate.
State TV reported that investigators believed that Lo Presti was planning to kill off supporters of a rival he didn't want to see get to the top of Cosa Nostra.
National anti-Mafia prosecutor Piero Grasso indicated in speaking to reporters in the northern city of Bergamo Wednesday that wiretapped conversations had helped investigators shed light on Lo Presti's strategy.
Grasso noted that some of those arrested on Tuesday had been convicted two decades ago in Palermo's "maxi-trial" of hundreds of mobsters, served long sentences and then resumed criminal activity when released.
State TV said that Lo Presti a few years ago had finished serving a 27-year prison sentence.
While Sicily's Cosa Nostra has been reeling under blows in the last decade, organized crime syndicates on Italy's mainland have grown increasingly powerful and violent.
Authorities have said that Cosa Nostra has been eclipsed in power and reach in international drug trafficking by the Calabrian 'ndrangheta, based in the "toe" of the Italian peninsula.
Camorra crime families based in the Naples area have been waging a terror spree for months, with some businessmen who have refused extortion demands among the victims of arson or killings.