A tip from the authorities in Andorra about a suspiciously wealthy Sicilian woman in their midst helped investigators solve an enduring mystery about one of Italy’s most notorious mobsters, known for his blood lust and business savvy.

On Thursday, the Italian financial police said they had seized more than $230 million in assets connected to the money laundering operations of the mobster, Matteo Messina Denaro, after an investigation spanning the Cayman Islands, Gibraltar, Lebanon, Luxembourg, Monaco and more.

Mr. Messina Denaro was a Sicilian gangster who for three decades eluded capture. He was finally caught under an assumed name at a cancer clinic in Palermo where he was receiving treatment in 2023. But when he died in custody months later, the Italian police still had few clues about his international investment empire.

Then came the tip from Andorra, the tiny independent principality between France and Spain.

The woman identified by the authorities there turned out to be from Campobello di Mazara — the same Sicilian town where Mr. Messina Denaro had enjoyed a comfortable life in hiding. And she was married to a high-ranking convicted drug trafficker who maintained close ties to Cosa Nostra, the Italian authorities said in a statement on Thursday.

Following that trail, investigators turned up holdings tied to Mr. Messina Denaro around the world, the police said. The investigation revealed “the substantial assets accumulated over more than 40 years through the reinvestment of proceeds from drug trafficking activities,” they said.

The investigation involved about 150 Italian police officers who worked in cooperation with counterparts around the world. They uncovered eight companies in Gibraltar, Spain and the Cayman Islands, more than 20 prime properties, including luxury resorts in Spain’s Costa del Sol, a stake in a bank in Lebanon and millions of dollars worth of investments in gold, the authorities said.

Mr. Messina Denaro was from the Sicilian town of Castelvetrano, but as big a player as he became in the mafia, he could never become the top boss. Under the gangsters’ code, that honor was reserved for Mafiosi who came from Palermo. Still, even while in hiding, he controlled the western Sicilian province of Trapani and built an international empire investing in legal businesses and assets.

The woman who unwittingly helped crack the case, her husband and a son, none of whom were named, are all accused of managing the mobster’s assets and were arrested, the police said.