Is Edward Snowden getting his vitamin D? Laura Poitras's new documentary Citizenfour shines bright light on the former National Security Agency contractor -- who did more than his own share of elucidating -- but still, we worry. As the images of a dark tunnel hint, things can get pretty bleak for whistleblowers.

Much of the film spans eight days in 2013 when the NSA defector is holed up in Hong Kong's Mira hotel. Composed and hyper-articulate at 29, Snowden briefs then-Guardian columnist Glenn Greenwald and reporter Ewen MacAskill about today's unprecedented reach of Big Brother. Snowden's disclosures touched off a global firestorm about privacy and covert surveillance in the post-9/11 era. Some 1.2 million Americans are under official scrutiny, we learn, with Poitras among them.

The Pulitzer Prize-sharing filmmaker came to the Snowden story when an anonymous correspondent tagged "citizenfour" approached her through a suite of encrypted e-mails. Her mystery sender planned to divulge the spying activities of the NSA and other intelligence agencies targeting citizens and governments in the US and abroad. After finessing a rendezvous worthy of a spy novel -- replete with a Rubik's Cube and cagey passwords -- Citizenfour outed himself as Snowden.

"I am not the story," the young informant admonishes when we meet him in the lanky flesh. Poitras scruples to honor his vision of foregrounding the issues at hand and not a tell-all personal profile. In one especially sobering tangent, an Occupy Wall Street adept details how an individual's doings can be tracked through such data links as a Metro card, bank and Verizon account. Yet the personality at the heart of Poitras's chronicle compels fascination in spite of himself. Snowden comes off as far more sane and sympatico than the mainstream media has largely allowed. That he shrouds his head while typing a password on Greenwald's computer may be overly cautious, but from where he sits it also may be a minimal precaution.

"You're not going to bully me into silence," he signals by way of explaining why he went public with his identity. Snowden knows enough about the media to know what he doesn't know, and to favor a strategy of entrusting his information to a trusted outlet.

The written word looms large in Citizenfour. From the get go, Poitras narrates the saga using title cards in the first person. And emails-in-progress serve both to impart information and to let us experience the unfolding drama as she ostensibly did. Whether all this flickering font adds to the suspenseful mood or begs for gumshoe action boils down to one's aesthetic druthers and attention span. Ironically, one of the film's climatic moments involves old-fashioned pen and paper. In Moscow, where Snowden was granted asylum, Greenwald scrawls news of another whistleblower considering a fresh round of intel disclosures. Snowdon's "holy shit!" echoes eloquently as the camera holds on images of the now crudely torn note, which is about as safe from the prying eyes of SIGINT as any communication in the age of mass surveillance may be.   

Citizenfour is the third piece of Poitras's post-9/11 trilogy including My Country, My Country and The Oath. It premiered at the 52nd New York Film Festival and opens on October 22.