so, if you had been a pedestrian crossing the street, the situation still would be the same? The idiot that hit you is saying "no, it wasn't me, it was the guy that left the scene"? You say you traded some paint, so does that mean there are some marks on his car? Should be easy enough to analyze that.
He probably already took it to the shop if he's trying to get out of this though I bet... A shame the cops didn't take your word for it at the scene and charge him and impound the car! I really hope this works out. What a douche. I hope he comes to his senses and realizes he won't be able to live with himself if he doesn't take responsibility.
Another thought. Sounds like a bad spot for a turn. Aside from the idiot's reaction, is it that surprising that he hit you? Are there any warning signs coming up the road about hidden driveways or anything? Obviously you shouldn't go ripping over a hill faster than you can stop in time to see what's on the other side...But maybe it's just a poorly designed road and that was a factor in what happened...