Yesterday, without putting a lot of time into it, I thought it showed he was rushed, and just left the car like that by accident.
But now that I've had time to think about it, I think:
Jennifer's Suburban being left with running lights on and in reverse at the park was carefully pre-planned. He wanted that car to appear as if it was running with no one in it, so it would be stolen (but oops! NC is much safer than Hartford or most places in Greece, so, it wasn't stolen in all those hours). He may well have left the car keys on the seat. Being in reverse would have made the rear lights show up more. If he left the ignition on, it may have automatically shut off after 15 minutes (most newer cars do to prevent exhaust poisoning when the car is left on but not moving). Just a thought - anyone know more about how that car works?