But perhaps the most important part of this de facto prologue concerns William Binney, a government intelligence analyst who turned whistleblower to protest abuses he saw taking place in the government’s actions after 9/11. For his troubles, Binney was raided by FBI agents who stormed into his house with guns drawn. The examples of Binney and others like him of course indicate the ridiculousness of the claim–made by President Obama and others in the government and media–that everything would have been fine if Snowden had gone through “proper channels” to make his revelations to the American public.

After contacting Poitras via encrypted email, and later asking her to involve Greenwald, the still nameless Snowden–“citizenfour” is the first alias he uses–asks the two to go to New York and await further instructions. He then tells them to meet him in Hong Kong (which he has chosen thinking it may be further from the eyes of U.S. intelligence than other places).

In my view, the film’s single biggest flaw lies in not saying at this point that Snowden sent Poitras and Greenwald massive numbers of secret files concerning government surveillance, which they were able to peruse before meeting him. In any case, these materials formed the basis of stories the two wrote from Hong Kong, Greenwald for The Guardian, Poitras for The Washington Post. (An account of what Snowden sent the journalists can be found in Greenwald’s book “No Place to Hide,” which deserves to be read in tandem with “Citizenfour.”)

We do not see Poitras and Greenwald meeting Snowden in the lobby of Hong Kong’s Mira Hotel (Greenwald recalled they were stunned at how young he was), but within minutes of arriving in Snowden’s room Poitras has set up here camera and begun filming. True to her cinema verite ethos, the filmmaker mostly remains unseen and unheard, leaving the questioning to Greenwald, and, beginning on the second day, another reporter from The Guardian, Ewan MacAskill.

The hour we spend with Snowden and company is matter-of-fact and in some ways undramatic, yet it is one of the most absorbing things I’ve ever seen in a film. (Having now watched the movie three times, I found this segment even more riveting on the third viewing than on the first.) What grabs you here is not, of course, the contents of Snowden’s revelations, which have been widely reported. Rather, it’s the sense of watching a small group of individuals embarked on an enterprise that they know is of tremendous historical import, yet also potentially dangerous and with no guaranteed outcome. In such a context, every small gesture, pause and decision can seem to take on great meaning, creating a constant sense of tension and discovery.