1. Do you have it in written from other dealer that car was in accident?
2. Did original Dealer provided you Clean Carfax before you bought the car?
3. Did original dealer listed this car as CPO and had Clean carfax before you bought it?
If your answers are YES;then go back to dealer and tell him that you went to other dealer and they told you that car was involved in an accident and it had clean carfax,why the accident was not reported? Return the car as lemon, file a complaint with BMWNA