I do a lot of wilderness hiking and this case has always bothered me. A remote trail could be a perfect spot to commit a murder since there would be little chance of encountering an unexpected witness. Ironically, the lack of people in the area presents a problem for a would be killer: any he did encounter, a fellow hiker on the trail, a driver he would pass leaving the area, or anyone observing cars in the parking lot, would be far more likely to remember them. From what I know about the case, there just happened to be no one hiking up the trail or driving into the trailhead area in the “window” of time after the murders were believed to have occurred. This was not a “well planned” killing; either by a killer targeting the woman specifically or just wanting to kill some random person. I think this was an unplanned impulsive act, possibly over something that occurred during an interaction with the women. The killer just got real lucky he didn’t encounter anyone on his way out. With no witnesses, no forensic evidence and no motive, it is the kind of case likely to go unsolved.
The big problem with the investigation was that it focused on the husband far longer than should have been necessary. Since he was the only “person of interest” all resources were directed at him.