Surely they could tell that you hit the car from the side at the rear............. as opposed to just hitting him up the ass......... Keep pursuing it, dont back down on this one. Take it to court, he will probably crack under pressure. At the end of the day, you have done nothign wrong, so you wont have to worry about keeping your story straight. If the witness was in your car, I think it can be put aside, as they are not independant. But yeah, a lesson for you and everyone really, I only learnt this from work (truck driver) but pick up a disposable camera and take pictures of the accident scene etc. if you should be unlucky enough to have an accident.