They've got the key to the car, but dont know who the owner is? StRaNgE...

I'd ask them to go into the car and dig out the registration, that'll tell them who owns it maybe? And then they can look through the apartment list and see who's car it is.

Its not likely that if you left a note on it he/she would find it, being that it sat there so long... Thats very weird that the apartment wouldnt be upset that there is a dead car in the parking lot with NO known owner... Maybe they'll give it to you if you move it for them...