Generally the following documents are required in order to open a damage claim:
Rental agreement from local rental company
Pickup and return document from local rental company
Damage report from local rental company
Final invoice from local rental company
Police report (mandatory in case of accidents, theft or vandalism)
Accident report (mandatory - in case of third party damage)
Photo of the damage
A copy of the credit card statement showing the rental company's charges (irrelevant amounts can of course be made unrecognisable)
Additional information can be requested depending on the type of claim.