Frankly I think he's massaging the media. It's gratifying to him in an almost erotic way. Taunting. He's got nothing better to do. He's got nothing else to do. He probably fancies himself smarter than all the players, thinks LE or the public will be impressed, influenced, manipulated. He may have some genuine confidence in that he could be fairly certain MM is unfindable, depending on how and when and where he left her. But most of his confidence IMO stems from whatever demons lurk in his nasty personality. Unquenchable love of self, utter lack of human empathy, pathological attraction to pain (other people's), etc, etc. Bet he was well on his way to the dark triad by age 12. IMO he can smell fear and it turns him on.
Grotesque. Devoid of humanness.
I believe he will be convicted by linkage. He filmed or documented or "confessed" (in some fashion before or after), used props or techniques identifiable in other crime scenes.
Tragically I think he kept MM for a time. And I suspect there's digital proof, linked to him via known crimes, and that poor MM had injuries inconsistent with survival/life.
If he's a trainee of hell, he surpassed his master
This is from a poster on WS... Pretty well my thoughts