What if the car IS his, but she was already gone? She should have been out if the lot within two minutes anyway. She may have already been gone away in a different car not caught on tape. I hate to think the car is his and he is not the perp, as that leaves us nowhere.
If the car was his and it happened as you posit in your hypothetical, then police would not be looking for it. They would know it was him. That would have been information that he would have relayed to them under questioning. If, of course, he were innocent.
As for the likelihood of it being another car, it would be on tape. She and the car in question were seen on the same tape within two minutes of each other. Another car would have been seen also.