reporter: so why would police focus on her? the beautiful socialite, ex-wife number two. she s very intoxicating. i think she was cold and calculating. reporter: maybe her former husband was worth more dead than alive? it s easy to blame the rich, beautiful woman. she s the person everybody loves to hate. but she is completely innocent. reporter: or maybe it was someone else entirely. he was obsessed with gary triano. obsessed with him. it s a case we ve investigated for more than 5 years. reporter: now a stunning new end. we go back on the rollercoaster. i m lester holt and this is dateline. here s josh mankiewicz with mystery on sunrise drive. reporter: spend a little time in tucson, arizona and here in the shadows of the majestic saguaros you ll find a thriving metropolis of a million people with a surprising small town feel. it s the kind of place where everyone seems to know everyone. and if you ask anyone from tucson where they were on nov. 1,