did you have a dashcam ? , the last 2 people I know who had a crash (both not their fault) took the guys details while he confessed, got home and phoned the insurance only to find a few weeks later the other person denied everything.
Either,
Phone the Police
or
Use a dashcam even in a hire car, take your own camera and it's a simple lighter socket and a suction pad and your away. I have 1 back 1 front, you can't believe how many tailgaters shift of your arse when they spot the rear camera in the back window