The Stewart Trial's Other Star
Profile of Peter Bacanovic, Martha Stewart's co-defendant and former broker at Merrill Lynch, who now plays key role as her chief alibi; he has consistently held that they had pre-existing accord to sell her ImClone Systems shares if stock fell below $60; their fates hinge on whether jury in their trial on obstruction of justice and perjury charges believes claim; he has remained mystery, disappearing from New York social scene, while she has started campaign to restore her public image; photos (M)
