But the film also captures the deep satisfaction that their work gave them. "I feel good in my human experience to know that I can contribute to the good of others," Snowden says in one scene. In another, Greenwald delights in a righteous "fuck you" to a spying government he regards as criminal and officials he sees as betraying core liberal principles. At film's end, we learn that Snowden is living with his longtime girlfriend in Moscow in circumstances far more pleasant than a Supermax prison, though how long he'll be permitted to remain there is anyone's guess.

History is rife with dissidents who took satisfaction in various causes—some worthy, others abominable. Snowden's critics will continue to insist that his actions were unjustified, no matter how earnest he appears to be about the nobility of his purpose. Yet I suspect that even they will find some merit in this film, if only for its footage. Seldom has the public gotten so intimate a glimpse at how a key figure felt and acted in private moments of profound historic consequence.

Though Poitras has a personal stake in the story she's telling, antipathy toward the surveillance state, and evident affection for what is surely the best source of her career, Citizenfour gives every impression of bringing a documentarian's ethic to the story it tells. In this regard, it compares favorably to the propagandistic stories the U.S. government has told in recent years after events as varied as the rescue of Jessica Lynch, the death of Pat Tillman, the killing of Osama bin Laden, and the Snowden leaks themselves. Additional facts about those events repeatedly contradicted the first accounts fed by officials to a hungry, credulous press.

If Poitras releases hours of raw footage from Hong Kong into the public record, as she told a Los Angeles Times interviewer that she may ultimately do, one gets the impression that her film will prove true to her source material. Meanwhile, mass audiences will soon get an edited look at Snowden that's at odds with much government propaganda about him, with effects on public opinion that remain to be seen.

"You ask why I picked you," Snowden wrote Poitras early in their correspondence. "I didn’t. You did. The surveillance you’ve experienced means you’ve been selected, a term which will mean more to you as you learn about how the modern SIGINT system works."

He went on, "From now, know that every border you cross, every purchase you make, every call you dial, every cell-phone tower you pass, friend you keep, article you write, site you visit, subject line you type, and packet you route, is in the hands of a system whose reach is unlimited but whose safeguards are not. Your victimization by the NSA system means that you are well aware of the threat that unrestricted, secret abilities pose for democracies. This is a story that few but you can tell."

I suspect most Americans who can imagine themselves being treated as the director has by their own government will leave the theater thankful for her film.