Don't stay stressed over it. The main thing is no one was hurt. Most of these property damage cases are "no fault" depending on what state you live in. The parking lot should have cameras that can be accessed by the insurance companies or the police. Some times they will release a tape of the accident if you ask the security guards or the parking lot management. That could be arranged. Check it out , you may be surprised when you ask. Certainly worth a try. Good luck and stay in peace and not pieces.