As a business owner I can tell you this dealer could absolutely be held responsible for the actions of his employee who had off hours access to the facility. He should be going after the employee legally and criminally and the refusal to give info is absolutely what the dealer has been told to do by his legal representative.
You need to lawyer up fast. It won't cost you a thing because a lawyer will take this one and accept payment out of settlement if you desire. I strongly suggest you will get more than a new car out of this if your lawyer handles it well and it will never go to court as long and no one gets to greedy on your end. But you gotta do it fast. No more contact with the dealership or anything directly. Only thru a lawyer. All it takes is for you to sound like you said the wrong thing and it can go the hell on you fast.