By International News Service HAMILTON, 0., Feb. 4.—The name of one man—‘Bob” Zwick, elusive ‘Fox’ of the southern Ohio underworld—loomed to the skies today as authorities prowled covertly in the shadows of gang land seeking to unravel the mys terious murder of John Marcus, one of the most notorious rack eteers of this region. Perforated with bullets, the hands and feet bound with picture wire, Marcus, whose criminal career was written on police rec ords the length and breath of Ohio, was found in a vacant house three miles north of here late yesterday. He had been dead, au thorities believed, at least three weeks.