|I think that the film is intentionally filled with enough contradictions and inconsistancies to make it work in multiple "whodunnit" configurations.
I agree, but only to a point. The open questions are (i) who actually killed Leonard's wife? (it could have been Teddy, Dodd, or a "random junkie," but not Leonard) (ii) how long has Leonard been carrying on his "investigation? In other words, to what extent is the "investigation" a self-delusion on Leonard's part to keep himself going, long after the crime has been "solved," and to what extent is it being prolonged as a result of Teddy's manipulations? Clearly Teddy smells, right? Leonard's grief over his wife's murder seems genuine throughout the movie, and also his horror when he thinks he's killed the wrong person. The filmmakers are not presenting a Leonard-as-killer, or Leonard-as-split-personality scenario--those are "Teddy's lies."