Deception lies at the center of “The Imposter,” Bart Layton’s canny but troublesome documentary, in more ways than one. It’s the tale of a French-Algerian con-man who successfully impersonated an American boy who’d disappeared a few years earlier, being accepted by the youth’s San Antonio family as the genuine article despite their physical dissimilarities. In the end, however, he claimed that the family had killed the boy, and only pretended to embrace him as their relative in order to cover up the crime. And in telling the story, Layton melds interviews and archival material with recreations so seamlessly that it’s often difficult to discern where the real thing ends and his reconstruction begins, so the film is rather deceptive, too.

The perspective from which the picture relates what happened is largely that of the imposter himself, Frederic Bourdin, who’s the main interviewee, explaining in great detail how he engineered the theft of young Nicholas Barclay’s identity. At times he comes across as proud of his cleverness, but elsewhere he engages in ostentatious self-examination, almost pleading for understanding and sympathy. That’s especially the case as the story reaches its final stages and his imposture is threatened, when he claims to have become suspicious about the motives of his false family members. But Bourdin’s penchant for saying whatever he thinks people want to hear makes one doubt his every statement, especially given that even from a jail cell he continued to engage in cruel cons related to lost children.

On the other side of the equation are the members of Nicholas’ family—his mother Beverly Dollarhide, sister Carey Gibson and brother-in-law Bryan Gibson are interviewed as well—who unequivocally accepted Bourdin as their kin despite obvious differences in his appearance. Were they so desperate to find the boy that they allowed their desire to overcome their good judgment? Or did they pretend to recognize Bourdin as Nicholas because his reappearance would help them continue concealing what really happened to him?

Then there are the law-enforcement officials like FBI agent Nancy Fisher, diplomatic officers like Philip French and social service personnel like Bruce Perry who got involved in the case and puzzled their way through the con. A particularly important role is assigned to crusty PI Charlie Parker, who became suspicious of Bourdin and has since been instrumental in investigating whether the family might have had a hand in Nicholas’ disappearance. In that connection neighbors of Nicholas like Allie Hostetler and childhood friends of the boy like Kevin Hendricks offer their observations on the family dynamic.

In the end “The Imposter” doesn’t offer a conclusive answer to the question of what happened to Nicholas Barclay. It’s like an extended version of one of those unresolved segments from the old “Unsolved Mysteries” series that ended with Robert Stack saying, “If you have any information, call….” But it certainly provides a fascinating glimpse into the mind of a cunning con-man who, for a time, got away with a cruel impersonation. And it’s just as cunning as he was in constructing the story to hold our interest.