Benedetto Cipriani was convicted Tuesday of conspiracy to commit murder and three counts of accessory to murder. He faces a possible life prison sentence.
Cipriani, 53, hired three men to kill B&B Automotive owner Robert Stears because he was having an affair with Stears' wife, prosecutors said.
Two of Stears' co-workers, Barry Rossi and Lorne Stevens, also were killed in the shootings.
Cipriani fled to Italy shortly after the killings. He was returned to the U.S. last year to stand trial.