The best of twists, the worst of twists
Now here's a first, for me anyway: the ultimate plot twist in a horror/suspense piece hinging upon 2 story details, one of them fairly clever (the visitor log); the other so utterly stupid (a "Final Destination"-style "sequence error") it up-ends the rules of its own exposition-- par for the course in Shyamalan movies, BTW.
With the former point, no trickery is employed, just the audience's trusting reliance on the cops inside the movie to know what they're doing, despite our pretty clearly seeing at the beginning a passenger who definitely didn't bother with signing the log. But to complete the misinterpretation reveal they just punt on the story so far, sort of a "throw out everything & recast it in a new context" approach; i.e. the cheap way out. Perhaps you're meant to think, "Aha, if I were going to fake my own death convincingly & own murder ambiguously inside a confined space that's how I'd do it"
One "clue" that had me laughing was the cops discovering DUI Marine's tool bag in the lobby restroom -- something which flunks even as a red herring, since the culprit has already gotten onto the supposedly sabotaged elevator.