I think a lot of times that lack of information leads to overthinking when, most of the time, things are much simpler than they appear.
- Carter references a very popular Christian movie called THE SHACK-a movie that came out not long after the girls were murdered-so the girls must have been taken to an outbuilding.
- The searcher asked Kelsi what color shoes Libby was wearing* so the girls must either have been nude or the shoe was off her foot.
- Carter, someone who's made other religious remarks, states that the girls are not how BG left them so it must mean that they were "posed" in death.
- Because nobody heard the girls scream, it must mean that BG used a ruse, like a fake badge, to get them to go "down the hill."
- BG's clothing appear "too big" for him, so he must have been in a disguise, including a fake nose and possible wig.
IMO the idea that this could've been totally random is so scary that it's also why many people think there was a social media connection and that BG followed them there-even though the family has stated that it was a last minute decision and no online activity has been reported (either through rumor or reporting).
Sometimes when you follow a lot of crimes your mind goes into overdrive. IMO this crime is a simple one. It's finding BG that's difficult.
* After reading more about the "shoe" incident it sounds like the searcher asked Kelsi what Libby was wearing (as in all of her clothing) and SHE was the one who replied and specified the color of her shoes. That's different than the searcher asking what color shoes Libby had on.