Evidence piles up on every side, but the very nature of interrogation of an event or person - by the media or by the courts - changes what we're looking at, since these processes need to simplify and pin down events which were probably intrinsically messy and ambiguous. It's interesting that the legal system seems to simply throw up its hands and walk away, but the media can't let go, and what happens to a person when the "official version" of them bears no resemblance to their self-image? "I'm not THAT Joyce McKinney" does sound like a throwaway, reflex, rehearsed lie, but it's nevertheless a lie that gets to the heart of the film's deeper concerns.
I agree with Jeff, though, that the "I'm not THAT Joyce McKinney" line is so transparently self-serving, and her incentive for using it so obvious, that it's hard to see it in any other light.
I guess I just didn't find McKinney all that compelling of a character or her story all that ambiguous. I've known people like her. You meet them and they seem nice, but it becomes clear before too long that you just can't believe anything they say. If she's telling the truth at times, good for her, but it's pretty obvious that her overarching narrative is a load of crap. I mean, regardless of what she says, or what Kirk might have told her, it's perfectly normal for a nineteen-year-old Mormon to go overseas on a mission.
I don't really see a lot of questions of identity that are brought up here, except in the most abstract way. I just see a delusionally narcissistic, mildly pitiable woman who did something long ago that a lot of people found fascinating, even though it's not all that interesting except as yet another example of the timeless truth that people will reflexively find young blond women captivating when they make the news in a context of sex and/or violence.
In the newest "Film Comment", Morris says something to the effect that McKinney collects men who are obsessed with her, and then says, "and I'm one of them!" And I thought to myself, reading this shortly after seeing the film, that
is what the movie's really about!