A Family Divided Over An Unsolved Murder (VIDEO)

More than five years ago, 40-year-old Shannon was found dead in her car at the bottom of a cliff. Highway Patrol initially ruled her death as a tragic accident. Two days later, based on the autopsy report, the sheriff ruled the death as a homicide. The case still remains unsolved.

Now Shannon's sister, Penny, reveals that she believes their father was behind the murder. "My dad has told me that if he ever wanted to get rid of someone, he knew how to get the job done," says Penny. "I believe that my dad murdered my sister because he thought he was going to get her business when she died."

Penny, who was away with her father at the time of the murder, explains: "I truly believe that my father has paid someone to kill my sister and make it look like an accident ... My dad is cold-hearted, controlling, and if you're in his way, watch out. My dad is very sick, and I can't let him get away with this if he truly has done this to my sister."

Her father, Ted, denies the accusations vehemently, and Dr. Phil reiterates that there is absolutely no evidence to support her theory.

Don't miss Thursday's Dr. Phil when Penny confronts her father. Click here to see where you can watch.