Not to mention possible involvement of curious animals and that sort of thing.
I've taken the circumstances of what happened that day, and between the murders and when they were found, and came to my own conclusion this was a well thought out set of crimes. The fact that the bodies were in the woods overnight would compromise critical evidence, namely DNA. Approximately 21.5 hours from TOD to discovery of the bodies, then securing of the scene, taking the bodies away, etc.
Cases I've seen where they were solved by DNA mainly revolved around crimes which happened indoors, as well as those involving bodily fluids, sexual assault, etc. One here in Fort Wayne was solved some years ago because the perp shed a layer of clothing after he shot someone twice during a struggle, so both the perp's and the victim's DNA was on the discarded clothing.
I'd imagine finding DNA on victims left outdoors, where the perp was at least somewhat careful about leaving DNA, might be difficult considering the exposure to the elements, so to speak.
JMO