I've been on that path and have seen that bridge. It's WAY back in there. I lived in Carroll County.
So is the theory Libby had communicated with the killer prior to the murder?
I admit I haven't followed all the rumors. The police have been very tight-lipped. My cousin is a sheriff deputy there and there is no info coming out. I think the theory is the killer lives in Delphi or surrounding area and they're waiting for him to reveal himself somehow.
ISP in an interview with KAK told him that the Shots account (to which KAK and his dad TK had access) was
the last non-family member to speak to Libby. Libby and KAK had both wiped their phones about one week before the murders. After the murders the Klines went to Vegas 'on vacation'. While in Vegas the Shots account closely followed the news of the murders.
LE knew about KAK's contacts with Libby right away. A search warrant for their home was served maybe 1-2 weeks after the murders. Apparently nothing incriminating concerning Delphi was found. Although LE knew of KAK's child porn activities right away, he wasn't arrested on those charges until 2019 or 2020. In the meantime, LE maintained that catfishing had nothing to do with the murders. Even after he was charged with many counts of child porn. That all changed in Dec '21 when LE strongly implied that catfishing and more particularly the Anthony Shots account has everything to do with the case. The thought by others is that KAK is way too slow and fat to have been the killer, but that Tony Kline, who is older, leaner, and much meaner and also had access to the account, could be the guy. No one else, to the best of my knowledge, has been shown to have had access to the account. LE concentrated on TK's connections to the account when they questioned KAK.
Problem is, neither TK nor KAK really appear to match the disguised appearance of BG, nor do their voices really match the "Guys...down the hill" audio.
Many theorize that KAK shared Libby's nude photos with another perv, who somehow enticed Libby to come to the bridge on the murder date. Problem is, the decision by Libby & Abby to go to the path/bridge did not appear to others to have been planned, but rather spur of the moment.
Other people think the killer is a local and the catfishing angle is just an amazing coincidence. There is one local who was on the bridge the date of the murder, and has apparently given LE conflicting statements about his time line on that day. He is also thought to have been the source for the 'first sketch' that was released by LE. He happens to look a lot more like the 'second sketch', which was created very soon after the murders, but wasn't released until 2019. Those who think he was the guy think he gave LE a description that closely matched BG to throw them off the trail. Problem is, I have never seen a motive for him that makes any sense.
Various other locals have also been mentioned as possible POI, even including the ex-mayor, who ended up being a the chief deputy prosecutor for the County after the murders. Derek, Libby's father, is not a POI; however, he is said to have been actively involved in the local drug scene when younger. Some have speculated that he later assisted LE in their endeavors, and there may be a revenge motive. To me, the killings seem way too personal toward Libby for that to be a motive, but who knows.
Others believe the the murderer wasn't local, but rather a random SK. The Prosecutor when the murders occurred stated that the murder scene was 'staged', and included 3 "signatures" of the type often seen in SKs, including one with some religious significance. The problem with this theory is that the murders were carried out with terrible efficiency, which points to someone with a very thorough knowledge of the path/bridge. Essentially, there is a two lane HW not far from the bridge, houses in either direction maybe 300-500 yards away, and a # of locals on or about the path that day. And the murders are known to have occurred between 2:15 and 3:00, with the killer or killers making a clean getaway. LE has stated that the killer "may be hiding in plain sight" and that people would be shocked when he was charged. To me, the best argument against it being someone form Carroll Co. is that there probably wouldn't be more than a few hundred men who could conceivably match the BG description, and none have been charged 5 years after the fact. Only 3000 people live in Delphi.
I say killer or killers because there is apparently disagreement in LE about whether there was only 1 killer, or more. It's pretty clear there was only one perp on the bridge. But there may have been 1 or more down the hill. Originally, LE said they were looking for a single killer. Now it's said that they 'go back and forth' over that issue.