gave michelle's family custody of his daughter. >> everybody we spoke with, all of them talked about how much he loved cassidy, and what a great dad he was. to just turn over primary custody, that was -- that was very surprising. >> reporter: investigators had heard enough. they believed they had a case. circumstantial, but a case. and three years after michelle young's body was found on the bedroom floor, jason young was charged with her murder. investigators and prosecutors knew that very little pointed directly toward jason young, but so far nothing pointed away. coming up, the case against jason young as an alleged killer and as a cheating husband. >> we basically just hung out at the house and had an intimate relationship for the two days he was there. >> cassidy was put to bed and a