Geneva - A Swiss man has been arrested in Geneva as part of an inquiry into an alleged plot to abduct the 12-year-old heiress to the Onassis fortune, police said yesterday. It was the second arrest in the case. An Israeli was arrested two weeks ago in Milan. Miss Athina Roussel is due to inherit some $2 billion when she turns 18. The money comes in part from her mother, Christina Onassis, who died when her daughter was two. Swiss authorities say they have issued arrest warrants against six other people, two of whom are former agents of Israel's domestic intelligence agency, Shin Beth.