Are you liable for another person's car if they refused to call the police to the scene and left and you didn't know you had to make a report?

==Complex question== There are a lot of unknowns in your question. One is left to wonder why you wouldn't eagerly call the police and/or file a report yourself after the other party (call him Party B) fled the scene, whether you were required to or not. One can only assume that there was little or no damage to your vehicle. We can also assume that the configuration of the accident was not favorable to Party B, which is why he was in a hurry to scram. (Or perhaps he wasn't where he was supposed to be at the time of the fender-bender and didn't want an official police report to document his location.) Whatever the case, if there was visible damage to Party B's vehicle, then you should have been concerned about potential reports and claims -- false or accurate -- he could make against you. But to try to answer your question, you may still be liable for the damage you caused to Party B's vehicle, but his fleeing the scene may mitigate substantially his claim against you because, by leaving, he assumed the risk of something happening to his car -- and intervening event that would break the proximate-causation chain. Further, leaving the scene of an accident with visible damage is a criminal act in some states and is, per se, negligent, which may also militate against him.