Prosecutors say Dr. Martin MacNeill was having an affair when he drugged and drowned his wife, Michele, in 2007. He has pleaded not guilty to her murder.
Today, the prosecution's star witness, MacNeill's 12-year-old daughter Ada, could take the stand, CNN's Miguel Marquez reports.
Prosecutors say Ada and her sisters will provide critical testimony against their father.
Prosecutor Chad Grunander says "Ada was the first one to find her mother in the bathtub and she can testify to exactly what she saw."
But putting a 12-year-old on the stand, and Ada was only six when she saw her mother dying or dead, will require sensitivity.