teens, perhaps her early 20s, had been beaten to death and left along an isolated stretch of the provo riverene was very graphic. you knew that she had taken one heck of a beating. she had -- she had suffered quite a bit. ♪ narrator: no conventional murder weapon was found at the scene, but it didn't take long to figure out what had been used to kill this young woman. six bloody rocks were found near the body. bonner: the rocks ranged in different sizes. we did come across one. don't want to say it was a small rock, but it was small enough that you could grab hold of it with your hand, and it appeared to have a handprint or fingerprint. narrator: the rocks told detectives straight away that they were dealing with what's known as a crime of opportunity. for whatever reason, whatever motivated that, he grabbed the nearest thing that he thought he could kill someone with and just beat her for a considerable period of time until she died. some rocks were as large as a small microwave that you might see on someone's kitchen counter -- very heavy, 50 to 70 pounds at least, were used to very angry,