Who was D.B. Cooper? After watching this engaging documentary by nonfiction filmmaker John Dower, it might be more fitting to ask: who wasn’t D.B. Cooper? Cooper’s 1971 hijacking of a Boeing 727 en route from Portland to Seattle—the only unsolved case of air piracy in the history of commercial aviation—has captured people’s hearts and minds for decades, so much so that the sunglass-clad culprit is regarded as a sort-of folk hero. The documentary recounts what happened during the hijacking, with reenactments based on passenger and crew member testimony (several of whom are interviewed in the film), and considers a few key suspects, plus a theory that Cooper died after parachuting from 10,000 feet into the Central Oregon woods on a dark, cold, rainy night. I love unresolved mysteries, but I’ve long been bored by this case; Dower’s documentary, though not a towering achievement of the form, rectified that, as he focuses on the people—from relatives of credible suspects to writers and amateur sleuths—for whom D.B. Cooper has become a preoccupation, if not an obsession. It’s astounding that there are several people whom one could reasonably suspect of being the elusive Cooper, with many more falsely claiming also to be him. Each suspect featured left compelling evidence, and a few have a stranger-than-fiction appeal that borders on uncanny. Dower succumbs to some of the more annoying trappings of such informational documentaries (and is a little too self-aware of the oddity contained within, with visual motifs reminiscent of Errol Morris’s Gates of Heaven), but overall this is compelling. Indeed, there’s a strange poignancy to Dower’s probings; several involved tear up either over memories of the incident or their sheer commitment to Cooper’s legacy. One can’t help but get a little misty-eyed with them.