Hi human
Sorry, I have no idea what he might have done with the car but any of your situations are possible, not able to think like him without considering the consequences. 20 miles in any direction from their house with the exception of east is full of roads and neighborhoods. And the weather in Colo draws both natives and newcomers to be out and about all the time. ALL days of the hours and night.
Sadly, a woman's body found by a bill board along the high way not too far from them a couple decades ago, but back then that stretch of I-25 was still a lot of fields, (agricultural, idle agricultural, and some cattle), the Watt's neighborhood did not exist til recently, just one building on that intersection (SW), a gas station that had a restaurant there on an off over the years-a mile or two or 10 in every direction, all fields.
Something from a link someone posted here a couple months ago has stuck with me in my mind. It said that the killers like these need the immediate "release or gratification" more than considering the required cover-up need afterwards. Then I recall that awful heavy metal band song he looked up the lyrics to afterwards (this is so disturbing to me).
I'd love to tell you more, I do not have any answers, and appreciate your question and opportunity to put some thoughts down in print instead of in my mind. I'm still saddened and disturbed about this though CW got what he deserves.