Bart Layton's "The Imposter" is a gripping true-crime documentary that removes a key element of the mystery from the equation with its title.
In 1994, 13-year-old Nicholas Barclay went missing in San Antonio. More than three years later, a young man surfaced in a remote village in Spain, claiming to be Nicholas. Overjoyed, the Barclay family welcomed Nicholas back into their life, ignoring or accepting that in his missing years, Nicholas had gone through a series of traumatizing events that transformed him into a different person.
The young man who returned from Spain was not, in fact, Nicholas Barclay. 
Layton isn't interested in taking the audience on an "Is He or Isn't He?" journey. The movie is called "The Imposter" and the movie has barely begun before the interview subject with the thick French accent, dark eyes and ethnically ambiguous olive skin begins his explanation of how he came to be confused with a much younger American boy with blonde hair, blue eyes and a light complexion. 
And what an explanation it is.
There have been and will be documentaries at this Sundance Film Festival that espouse more admirable messages or that exhibit more confident artistry than "The Imposter" does, but it's hard to imagine any film, narrative or doc, unspooling a more gripping, twisted yarn.
Imagine "F For Fake" mixed in with a bit of "The Talented Mr. Ripley," only theoretically all true and you have a good sense of the appeal of "The Imposter."
There's an approach to "The Imposter" in which the movie is called... I dunno... "The Son"? Or "The Missing"? In that version, Layton would have attempted to keep the audience guessing about Nicholas' identity allowing the horror of this nightmare scenario to build slowly. In that version, the audience would start in a place of darkness and expect gradual illumination. 
Layton's approach is practically the opposite. We're introduced to the Barclay family and to the eponymous Imposter simultaneously. The Barclays and The Imposter recount their stories in a matter-of-fact way that belies the incredible nature of what occurred. So as The Imposter reveals how he duped the family, the family recounts, without self-awareness, their emotions as the story developed. The technique gives viewers the illusion of dramatic irony. We initially roll our eyes and laugh in knowing bemusement at their obliviousness. We study their recounting of a story in which they know the ending as much as we do.
Initially we feel superior to the Barclays. How could they possibly not have realized? Why would they possibly let themselves be used in this way? But then you start thinking your way through those questions and "The Imposter" begins to feel more and more like a meditation on grief and the desperate need for resolution and self-delusion. And then just when you think that you've figured out motivations and worked yourself into a position of sympathy, "The Imposter" changes gears as an FBI agent and a private investigator begin to have their own suspicions about the Barclay case.
The Barclay case hasn't exactly gone undocumented. It was widely reported on when the story broke and it was even adapted as a French feature film in 2010.
In addition to the structuring choices, what makes Layton's approach stand out is the sheer access he was given. The Barclay family had never been this open previously and while their versions of events isn't without rationalizations and possible agendas, that's really what "The Imposters" is about. There's no second of interviews in the movie that don't leave you thinking, "Why would that person be saying that thing in that way?" or "Who does that interpretation of events benefit?" There's so much across-the-board complicity afoot in "The Imposter" and for many viewers, this will be a source of discomfort.
For other viewers, The Imposter's degree of on-camera presence will be a source of discomfort. What he did is simultaneous reprehensible and also remarkable and, as you'd guess, his preference is to accentuate his own brilliance. Layton's choice is to give him enough rope to hang himself with, except that the history of the case didn't lead to literal or metaphorical hanging. He's smug and reptilian and there's a strong possibility you may find yourself impressed by him and then feeling dirty about it. Like I said, it's all about complicity and in any story about a good hoax or swindle, audience complicity is nearly mandatory.
The blurring between objective documentary truth and narrative subjectivity  gets tweaked with Layton's use of reenactments. "The Imposter" was shot by Erik Alexander Wilson ("Submarine") and edited by Andrew Hulme ("Control"), who both bring feature polish to their work. The reenactments have a stylized veneer, but Layton uses the talking head audio to confuse the issue. There were times watching "The Imposter" when I began to doubt that anything I was hearing and seeing could possibly be true, but then there were other times that I temporarily confused reenactments with real footage.
Sundance documentaries often get purchased for weird purposes. I'm still waited on the scripted version of last year's gypsy boxing documentary "Knuckle." I'd make "Searching For Sugar Man" into a narrative film in a second and I already know who I'd cast in the lead roles. And I'd say that "Imposter" is another doc that's ready-made for a semi-fictionalized retelling, but with a version that's already this tightly plotted, "The Imposter" should be able to strike a chord even with an audience that fears documentaries on principle.
A long-time member of the TCA Board and a longer-time blogger of "American Idol," Dan Fienberg writes about TV, except for when he writes about movies or sometimes writes about the Red Sox. But never music. He would sound stupid talking about music.