Nothing in her career as a documentary filmmaker could quite prepare Laura Poitras for an encounter in a luxury hotel room in Hong Kong in June 2013. It was there, amid absolute secrecy and after months of encrypted communications, that she met Edward Snowden. The once-anonymous contractor for the National Security Agency was about to become the world’s most famous whistleblower, leaking classified documents that exposed the unprecedented global and domestic reach of the agency’s surveillance programs.

“Being in the hotel room, I had an experience I had never had before,” said the filmmaker, who spoke after introducing a screening of “Citizenfour” at the New York Film Festival, where the film premiered Oct. 12 to a long, loud standing ovation. “There were things I filmed that I couldn’t remember that I filmed, and I saw them later in the footage. I just blocked them.” Although she remains behind the camera, Poitras was joined in the sessions by journalists Glenn Greenwald — to whom Snowden had likewise reached out and the filmmaker persuaded to participate — and Ewen MacAskill of the Guardian. They would become the conduits for the release of Snowden’s explosive revelations. (Many of the further revelations came in a series of Pulitzer Prize-winning stories written by Barton Gellman that appeared in The Washington Post.)

“There’s a conversation when Glenn talks to Snowden about coming forward, and the camera goes back and forth, and I actually didn’t remember I filmed that, and for me it’s the most powerful scene in the film,” said Poitras, 52, a poised figure in jeans and a black jacket that would allow her to blend into any Manhattan crowd. In the scene, Snowden insists he will go public as the source of the NSA leaks that the journalists will release regardless of the consequences. It’s a palpably electric sequence, which would be the core of any fictional drama. In this case, though, the action is perilously real, and the camera isn’t only capturing a historical event, it’s part of the making of it.

“The choice that he’s making could end his life,” Poitras said. “I’ve worked in war zones with bombs going off, and I know, ‘Okay, that’s the moment.’ I know that’s the one where all the emotion is contained. In this case, my brain, whatever those defenses were, just blocked it out. I felt we were in a state of free fall, not knowing what kind of landing we’d encounter.”

When “Citizenfour,” which takes its title from a codename used by Snowden to identify himself to Poitras, opens Oct. 24, it will introduce audiences to a mild-mannered and quick-witted computer expert who is variously considered a traitor or a hero but whose image has been inevitably distorted by much of the news media. “I think there’s enough evidence on the table you can make your own decision,” said Poitras, whose measured approach frames in intimate and vulnerable terms what might have been sensationalized. “We wanted not to be influenced or feed into the frenzy around us but stay true to material and the human drama. It’s really about Snowden and what he chose to do.”

Still from the Edward Snowden documentary, CITIZENFOUR. (Courtesy of RADiUS-TWC)

It also is often quite funny, as Snowden’s tech-geek mannerisms underscore some of the absurdity that comes with living in a real-life Jason Bourne thriller. At one point, as a rational paranoia compels him to hide his laptop as he types, he throws a blanket over his head. He calls it “my mantle of power,” causing everyone to break up laughing. Such instances eased the tension. Though Poitras said she felt much safer once they began releasing Snowden’s information, she had no illusions they hadn’t been tracked.

“They look at flight manifests,” she said. “The intelligence communities knew by that point. But I think one of the reasons the story had the impact it had is Glenn worked at a really fast pace. The U.S. government couldn’t respond in time. We caught them a bit on their heels. They didn’t expect Snowden would reveal his identity, so we controlled the narrative for a while.”

The film completes a trilogy of documentaries about America after 9/11 that include the Academy Award-nominated “My Country, My Country” (2006) and “The Oath” (2010), films that took Poitras first to U.S.-occupied Iraq and into contact with Abu Jandal, a Yemeni taxi driver who had once been a bodyguard for Osama Bin Laden. The filmmaker would find herself on a secret terrorist watch list that would lead to multiple detainments whenever she tried to enter the United States. “I’m certainly not carrying any footage across the border with me or any source material or any notes,” Poitras said of her recent trips to the United States from her adoptive home in Berlin. “I’ve learned my lesson.” It was her persistence in the face of these actions, which had been publicized by Greenwald and other journalists, that suggested to Snowden that he could trust her.

“She is taking on the most powerful nation in the world and has been repeatedly targeted for doing so,” said Jeremy Scahill, a co-founder with Poitras and Greenwald of the Intercept, an online investigative journal, and writer-producer of the Academy Award-nominated documentary “Dirty Wars.” “This boils down to the power of one woman’s camera against the entire national security state.”

Poitras already was at work on a film about that security state when Snowden first contacted her in January 2013. That material includes footage of former NSA official and whistleblower William Binney, speaking out against the surveillance state, and of the construction of the massive, NSA-managed Utah Data Center near Bluffdale. The film establishes tension from its opening glimpses of encrypted data on a black screen and computer messages between Poitras and a yet-unidentified Snowden. Sinister, minimalist music composed by Trent Reznor and Atticus Ross (Academy Award winners for their score on “The Social Network”), fills the soundtrack, instilling a sense of nervous unease that accompanies the road to Hong Kong.

“Laura exemplifies that delicate intersection of art and journalism that the best non-fiction films often occupy,” said David Wilson, co-director of the True/False Film Fest, a leading documentary-oriented festival based in Columbia, Mo., which showcased the filmmaker’s work in 2010. “It’s telling that Edward Snowden picked Laura to trust in revealing his secrets, though, as he says, she chose herself. She did that by being honest and brave and willing to go to any length to tell a story correctly.”

“Citizenfour” concludes with a final Snowden encounter — and a personal note: His girlfriend, Lindsay Mills, is revealed to have joined him in Moscow, where he lives on a three-year visa after fleeing there from Hong Kong.

“I make films about people,” Poitras said. “I don’t know if films about people change policy. I would hope that our elected officials would respond in terms of increased transparency and accountability for these actions, and not just around surveillance but other things like drone strikes. The government has moved in directions that are pretty radical. The level of secrecy that we have is very frightening.”

Dollar is a freelance writer.