Auto Insurance Claims: Proving fault, rear axle, left turn

Question
I was in a double left turn on the outside lane, the car in the inside left lane hit the back of my car. Hit me and took off. Caught up 4 miles away. Now his insurance company and mine are the same. His story is completely opposite and they won't reimburse my deductible. I want to go into mediation because he hit me. How can I prove his fault? They say because there are no witnesses his fault couldn't be proven. I might have had a witness but since I had to chase him down I was unable to obtain witnesses. Can you give any suggestions?  Thanks

Answer
Based on your description of the events and damage and where his car hit yours, I would assume he was at fault. And based on the fact he fled the scene, your case has that much more merit. Usually the fault belongs to the person who hit your car behind the rear axle.