Remember Deep Throat, the mysterious source who helped to unravel the Nixon administration’s Watergate scandal by meeting a reporter in a parking garage? Citizenfour begins with a series of cryptic email exchanges that makes that secrecy precaution seem like child’s play.

“This will not be a waste of your time,” a would-be informant assures documentary filmmaker Laura Poitras. When Poitras and a couple of reporters for a British newspaper finally meet the informant in a Hong Kong hotel, this proves to be the understatement of the decade.

The man is Edward Snowden, a consultant who until recently had been working with the National Security Agency. He has an astounding story to tell about how much the government has infringed on the average citizen’s privacy in its efforts to fight terrorism. As Poitras’s camera watches and the reporters take notes, he proceeds to do just that.

By now, the world has already learned what Snowden told Poitras and reporters Glenn Greenwald and Ewen MacAskill in that hotel room. CBS’s 60 Minutes, for example, not only scored an interview with Snowden but followed it up with an NSA response that sought to make Snowden’s character, rather than his charges, the real story (a strategy that will seem eerily familiar to anyone who’s seen Kill the Messenger, a recent fact-based film about the media’s response to a reporter who sought to reveal another government secret).

In some respects, then, Citizenfour has been upstaged by news coverage of Snowden and his revelations about NSA spying. On the other hand, it offers something the news media can’t: a behind-the-scenes account of just how those revelations were released in the first place.

We watch as Snowden, casually dressed in a T-shirt and jeans, tries to ensure that the room and its occupants’ electronic hardware haven’t been infected with eavesdropping devices. At one point, he goes so far as to pull a hood over his head and shoulders while working on a computer.

He would come off as paranoid, but given what he knows and what he plans to divulge about what he knows, it’s easier to assume he’s merely taking reasonable precautions. 

In general, Snowden appears to be a man driven by principle and little else. He calmly admits that he expects the government’s response to his revelations will forever separate him from his family. Other than shedding a tear or two, he’s nearly as stoical when he talks about the girlfriend he left without warning or explanation because he didn’t want to implicate her in what some have called an act of treason.

Why did Snowden commit this act? He explains that he believes government surveillance that compromises our privacy also compromises our freedom. But though the filmmaker and reporters have no trouble getting him to explain the “whys” of his behavior, they’re less successful at learning the “hows.” In particular, we’re never told just when he began to seek asylum in another country. Was that his plan from the beginning, or was it a reaction to the government’s intention to charge him with espionage?

Citizenfour may tell us some things we already know, while leaving unsaid other things we wish we knew. But it’s essential viewing for anyone who wants a fly-on-the-wall perch from which to watch history in the making.

Rating: 3½ stars (out of 5)

Citizenfour, rated R, opens Friday (Nov. 14) at the Gateway Film Center in Columbus.