year for her family. cassie's mom left her with someone she trusted. while she was gone, cassie suffered a severe head injury. i can tell you as a doctor, but more importantly as a father of three young girls, this story really got to me. how cassie got those fatal head injuries remained a mystery for years. but to some in cassie's family, the facts didn't add up. turns out they were right. here's randi kaye. >> reporter: in the morning of january 18th, 2001, the only person at home with cassie was her mother's boyfriend, former marine, william veech. just before 10:00 a.m., veech called 911. by the time paramedics arrived, cassie, just 17 months, was unconscious. doctors described her brain as jell-o. there was severe hemorrhaging, lots of blood. doctors immediately suspected shaken baby syndrome. but when police questioned veech, seen here in this interrogation video, he denied harming the toddler. veech told police cassie was in