I think, the killer is someone, who is proud to do the crime all by himself and in a wink and to escape police in every state, he did a felony (maybe, we don't know). Nevertheless he could have had a good friend, who helped him cleaning up the scene in Delphi and covering his tracks. IF he had some help (someone, who knew the area/terrain), he could have brought back the girls from another crime scene to RL's property.
..... My laptop is overheating ..... a moment please.
ETA:
I think, where ever he is, he comes around verrry quick, acc. to Carter. His special method might be, that he puts his victims always to another second/third crime scene: in IA 25 miles from the place of abduction (near the bank of a bending creek), in IN 500 ft from the place of abduction and even bringing the girls back (ie from a shed/shack) to a previous crime scene (near the bank of a bending creek). Whether bicycles (IA) or Libby's cell phone (IN), he doesn't pick things up, which would betray traces of the first crime scene. Just like Carter said, it's all about "power and control". He knows, what he is doing after the crime and he is playing around with the police. The victims should have been found, but certainly after several months only (decomposition). Maybe, he thought, RL's place was searched already and the property owner would find the victims one day, months later.
I think, BG is very proud of his craftiness avoiding the impression, he might be a killer or even a SK.
All IMO and MOO. Of course!!, I don't know and police didn't confirm, IA and IN cases have a connection.
I can't help: the sweet girls from IA are always on my mind in connection with the sweet girls from Delphi/IN.
What I don't know, is: why murder, why Abby, why Libby, why a little innocent girl at all.
Why violence, why "staging" (IF). Question mark over question mark.