Just on a practical note - would a Dashcam have helped you in this instance?
My understanding is where it's an option, they'll record an event if it detects an impact. If the camera was mounted on the windscreen I doubt it would be able to film the offenders number plate from that angle unless it occurred when they were leaving and it recorded them driving away.
I will eventually buy a dedicated Dashcam, in the meantime I use my iPad mini which runs 
iSymDVR
Here's a sample video:
iSymDVR test (Enhanced) on Vimeo