Anything is possible, of course, but in my uneducated opinion, that which is the most common, most simple scenario is most often the correct one. While it is of course conceivable, I just don't see someone abducting two girls, and then returning them deceased to the exact spot where searching was still ongoing (reportedly family stayed out overnight.) It just doesn't ring logically to me. When I think about the most likely scenario (IMO IMO IMO) this guy was stalking the area to either assault, kill, or both. He was easily able to subdue both of them by threatening one with a weapon and telling the other that if she screamed or ran her friend was dead. Why pick two? Maybe he didn't see the second girl. Maybe he wanted two. Maybe he was stalking one of them rather than the area. Certainly no one but BG knows. March them down the hill and across the creek at a low point, do whatever he did, and leave. 100% my own opinion, but it always seems to me like the simplest answer is the most common answer. For every pig farmer feeding bodies to his pigs, serial killers burying bodies on his property, or ritual killings, there are probably hundreds if not thousands of straight forward murders.
As to why didn't the searchers see the bodies the night of the 13th, RL reported being asked that night (WISH tv link) if they could search his property. Twilight in Delphi that night was 6:47pm according to the calendar I posted below. If the searchers even made it on to his property that night, they were working with the limited beams of flashlights and a large, brushy area with a lot of leaf cover. I have participated in a few evening searches, and many more daytime ones, usually for an older adult with dementia or a child with autism who left their home, a handful of runaways, as well as a few missing persons reports that turned out to be suicides or ODs. A few times we absolutely missed what we were searching for by mere feet even in the daytime, due to leaf cover, not having enough searchers, inexperienced searchers, searchers not using a grid or line search but willy-nilly looking, and one time because we didn't look up despite the searchers being in exactly the right place. Can't provide links to those, as they were my personal experiences.
My long winded point was, I would be much more inclined to believe they were simply missed in the search that night, rather than someone going out of their way to return their bodies to that precise location. YMMV, and I genuinely appreciate all of these differing opinions because at the end of the day, none of us know the truth, but we all care a heck of a lot about these girls and getting justice for them.
http://wishtv.com/2017/02/16/police-question-multiple-people-in-delphi-girls-murders/
http://www.sunrisesunset.com/calendar.asp