investigates on suspect michael may have been responsible for both deaths and in the search for evidence they were about to exhume elizabeth's body. could the old case shed new light? continuing with our story, here's dennis murphy. >> as time went by, margaret blair had come to accept michael peterson's explanation of her sister's death years before, a tumble down the stairs in a german townhouse. >> i just believed what i was told about the cerebral hemorrhage and, you know, i'm presuming that a doctor had, you know, made this diagnosis. >> but when she learned that kathleen had also been found dead at the bottom of a staircase, margaret began wondering anew about how her sister died. she started reaching out elizabeth's old friends from germany. >> when i talked to her friends, i found out that blood had been dripping down the walls. well, that doesn't happen when you have a cerebral hemorrhage. >> authorities in north carolina were thinking the same thing.