Police arrested fugitive Sicilian mafia boss Matteo Messina Denaro's brother-in-law Gaspare Como in the western Sicilian port city of Trapani on Monday.
Police also seized a clothing business and a property in the nearby coastal resort of Triscina linked to the probe and to Como's arrest.
Como is suspected of fraudulently registering assets in the probe.
He is married to Messina Denaro's sister Bice Maria Messina Denaro and has prior convictions for organized crime and extortion.
Police have since 2012 impounded goods worth some 200,000 euros from Como, including real estate and luxury vehicles all fraudulently registered, according to investigators.
Fifty-three-year-old playboy Messina Denaro has been on the run since 1993 and is estimated to have killed at least 50 people.
"I filled a cemetery all by myself," he said to have once bragged.
He sealed his murderous reputation by slaying rival boss Vincenzo Milazzo from Alcamo and strangling Milazzo’s three-months pregnant girlfriend.
Messina became the head of the Sicilian mafia after the arrest of Bernardo Provenzano on 11 April 2006 and Salvatore Lo Piccolo in November of 2007.
