Witnessed an accident - mild one, luckily

Ah, but I didn't see. I heard the crunk and saw the immediate aftermath.

Events as they rolled:

Cait slows and becomes first in the queue for a right hand turn on a 4 point junction with 2 dedicated lanes, one for straight on/left, one for right. It is dark. It is raining.
Crunk!
Look back, person on moped on road surface
Cait, incensed that the car is driving away from the crunk does what in retrospect seems pretty cool. Incensed, I put my hand up in the universal "Stop" motion and yell "STOP!" in a big, loud, incensed sort of voice. The car stops
The lights change, I notice that there's no one with the injured person yet, and it's very dark, I wave to the car beginning to travel in the traffic incident victim's direction "Stop! Stop!"
there's no one with the bloody victim! I grab the bike and begin to pelt toward them, suddenly there are 4 other people at the victim and FUCK! FUCK! The fucking driver is driving off!

...I totally ballsed it up, through doing a stupidly obvious thing - trying to help, where I was already bloody helping! Twat!

Victim = hurt ankle, girl, in shock saying "I'm fine, I'm fine", refused help for so long you kind of reach a point of diminishing returns and back off, so I left home.

Here's the question though - what should I do?I didn't get his/her plate, I didn't actually see the incident... McK thinks the whole thing will be on CCTV. Possibly? The plan is to call the local cop shop and see what they say. Maybe given that they have evidence on film (if they do) they'll be able to get the stupid bastard for dangerous driving purely "because", if you see what I mean.

Who knows?

Here's a lesson. Cycling in the dark and the rain, I'm lit up like a bloody Christmas tree. you couldn't miss me. Girl on moped: had 1 light at the front of the moped, and was wearing black all over.  I don't know that it hinged on that, but apparently the driver suddenly began to turn out of the lane and veer right, therefore banging the side of the vehicle straight in to her. It is possible that s/he didn't look, and didn't see her, but she was also somewhat non-seeable anyway.

So. Cycling home in the dark and the wet.

(Nervous).

Update later:

Without a victim, even though the crime might be on camera and therefore there are two witnesses - a human and "silent" one, there can be no crime report, apparently. In this day and age that is completely nuts! I mean if you clearly have electronic, untampered evidence, and you clearly have a witness happy to step forward and you clearly have a driver who is willing to drive away from a victim of their own crime, who is therefore a danger to other road users... ???

However, that's the way it crumbles, I guess. Hmph. They've taken the details I had, and if the victim comes to the station to report it then they'll give me a toot (ie: that's the end of that).