The Chameleon, starring Ellen Barkin as the druggie mother of a missing son, Nick Stahl as his violent druggie brother, Emilie Ravin as his weepy sister and Famke Janssen as a cop of some sort. The plot starts when a boy speaking French claims to be the missing son. His sister comes to France, positively identifies him and he goes home. The movie takes a twist when he is exposed as a fraud. The resolution is that everyone identified him as the missing son so that he could provide an alibi. For the brother? Or possibly the mother?
The interesting thing is that after I saw this I found there is a new documentary out about the true case that inspired this. (The real case took place in Texas, not the more colorful Louisiana.) Like Monster or Daniel y Ana, the discovery it's supposed to be about real people is disconcerting and makes me uncomfortable. Accusing real people, instead of characters, of murder is serious business. The movie is indie solemn but I suspect takes far too many liberties with characters to feel right about fingering a real person.
Of course the thing about Monster is the way it exonerated the Wuornos' girlfriend and the thing about Daniel y Ana was the hysteria mongering. But the slapdash Hollywood approach to fact (shared by indies) makes movies about private figures seem intrinsically suspect. Public figures we usually know enough about (since they're public) to catch "artistic" deviations.
PS I saw an EW sidebar on this and they didn't even seem to be aware of this movie.