I’ve become convinced (for the time being
) that BG did NOT know he had been recorded, heard Libby’s cell phone ringing when DG first called, then silenced it and left it where it was because he knew time was up and he had to get out of Dodge. I think BG purposefully left Libby’s cell phone because he understood how tracking works. He knew he shouldn’t take it with him and he flat out didn’t have time to destroy it (throw in water, etc). Thinking what’s the harm of leaving it if he didn’t think there was any incriminating evidence on it.
I do think it’s possible he was still trying to leave the scene (clean up, place things the way he wanted it perhaps, etc) when DG had already entered the trails starting to look for the girls.
MOO.