I was thinking about the half-truth of telling LE that YZ panicked when he took a wrong turn and so he let her out.
It made me wonder, perhaps there's more truth to that even still, perhaps he did let her out somewhere, very far away, and after subjecting her to whatever he wanted to do to her, essentially left her for dead. Alive, but barely, or somewhere that would be fatal to escape from, a huge open space/rocky terrain/whatever jumped in his car and sped off (just like he did in the video, he put his pedal to the metal, I;m sure if there was no speed limit, that ****er would have driven off with her even faster!) leaving her.
That way he doesn't have to worry AS MUCH about a murder charge, and can sort of use the 'she panicked, I let her out' alibi, because it wouldn't really be too much of a jump (if you know what I mean.) He can be brazen and unshaken and go to a vigil because hey, all he did was drop her off somewhere, right?
On a different level: the audio recording - do you think that he confessed to more? IF he was telling someone wearing a wire, wouldn't they have pushed him to finish the story off? "What did you do with her in the end?" that seems the obvious question. Maybe that's when the threat came in. I don't know.