The death of a possible defense witness could deal a blow to Scott Peterson, charged with the death of his wife and unborn son.
Seventy-eight-year-old Vivian Mitchell was Peterson's neighbor. She had said that she saw Laci Peterson alive hours after police claim her husband killed her.
Her family says Mitchell died yesterday from natural causes.
Mitchell's account would have been preserved if she had testified at Peterson's preliminary hearing, but defense lawyers didn't call her. Neither side would say whether Mitchell testified under oath at any other point.