If it was Beth that rented the car in her name with her CC there is NO way she would leave it with a friend to drive back.
Whatever happened, happened Sunday night. If I were LE I would be looking at J and R's activities late afternoon and Sunday evening.
Very perplexing case.
On the FB page, Mary posts that she believes Beth rented the car, not J. She seems pretty certain, but do not know how she knows this to be fact. Still a question mark for me