Journalist Glenn Greenwald's name is indelibly associated with the explosive National Security Agency disclosures that began last year. But filmmaker Laura Poitras is the one who engineered them. After Greenwald brushed off Edward Snowden's initial attempt to contact him over encrypted email in December 2012, the NSA contractor turned to Poitras. She pushed the daring trip with Greenwald to Hong Kong to meet the source.

Poitras was in many ways the perfect point of contact for Snowden. She was a filmmaker who had already explored the post-9/11 world in two documentaries, one of which focused on Iraq and had landed her squarely in the sights of U.S. authorities. She was subjected to so many searches at U.S. border control that she moved to Berlin to protect her footage.

When Snowden reached out to her in January 2013, she was in the beginning stages of a movie about domestic surveillance, focusing on four ex-NSA employees who had blown the whistle on the agency. After the disclosures, she shifted the focus of her project to focus on Snowden almost exclusively.

Holed up in a Hong Kong hotel, Poitras, Greenwald and Guardian reporter Ewen MacAskill grilled Snowden about the documents he provided and sought to paint a portrait of his motivations. A year and a half later, after Poitras shared a byline on many of the articles about the NSA disclosures, her coverage of the Snowden saga now moves to the big screen.

"Citizenfour" takes its name from the codename that Snowden used in his early emails to Poitras, before their partnership exposed to the world the vast extent of the NSA's mass surveillance. A gripping and intimate document of those eight tense days in Hong Kong -- and of the reverberations they sent through the world -- it opens in theaters on Oct. 24.

This interview was edited and condensed for clarity.

Tell me what went through your mind when you got the first email from Snowden. You didn't know it was him at that point.

It was January 2013. His first email was really simple: 'Hey, can I get your key?' I had a public [encryption] key, so at least I knew what he was talking about. And so I sent him a key and I said, 'Here you go, who are you?'

Then I got an email which was sort of the holy shit email, where I was like, if this is legit, it's a big deal. It's dangerous. It's dangerous for the source, it's dangerous for me, it's dangerous for everyone, we're going to piss off a lot of powerful people. My instinct was it read like it was legit, but then I also was careful -- it could be a set-up, it could be entrapment.

And was that fear of entrapment informed by your previous experiences at the border?

I thought I could be a target for entrapment because I've been stopped at the border so many times. Or I thought that maybe somebody that I was filming with could be the target, and I was kind of a conduit for them. I was just being careful, just basic due diligence.

I was already, by the time I was contacted, a bit seasoned in terms of dealing with government harassment. I wasn't naive. So I made sure that I had a healthy skepticism. But I was pretty convinced, pretty early, that it was legit.

Why were you working on a film about surveillance in the first place? Your other films have been so outward-looking.

I've been working on this post-9/11 trilogy. I made a film first about the Iraq War, and I did a film about Guantanamo. When I was working on the Guantanamo film I knew that I wanted the final piece of this to come back home, to say that these are not films about the Middle East, these are films about America and American power.

Glenn's work, I was really reading it a lot. And I thought that's really interesting, this guy who's writing for Salon.com is doing it so off the grid and causing so much havoc and applying so much pressure and speaking so uncensored, so I thought, wow, this is a new breed of journalism.

I didn't know where the story would go or where it would take me but I got on a plane and I went to Rio. It's the first scene in the film, and that was two years before we went to Hong Kong. I just had a hunch that this guy was doing something interesting.

Clearly my impression of what Glenn was doing was actually something very similar to what Snowden felt, and why he reached out to Glenn.

I love the tick-tock in Glenn Greenwald's book of him getting on the plane to Hong Kong, where he details what he's thinking. What were you thinking on the way there?

I would say I was really nervous. I was also really determined to go, and I was also really determined not to go alone. Going alone just sounded like a really bad idea. A documentary filmmaker getting on a plane to go to Hong Kong to meet the source of these kind of claims without any institutional backing? Probably not a good idea.

Glenn and I had a meeting in April where I basically did a debrief, and I said, 'Look, I have been contacted by a source, he says he has documents, do you want to work on it?' Glenn immediately said yes.

When we were in the taxi traveling I was just really glad that it was finally happening. I felt that there were a lot of people who were trying to talk me out of it.

I thought it was essential to meet [Snowden]. I wanted to know who he was, I wanted to know his motivation.

Those days in Hong Kong are kind of the core of the film. They're just incredibly intense and amazing to watch. What was going through your head when you were there in that hotel room?

I was very aware that we could have a knock on the door and it could be all shut down. It felt like a bit being in a freefall. There was a clock ticking that Snowden had left the country.

It felt really urgent to publish as quickly as possible, and I think we both felt -- and Snowden felt -- that [he should get to] say why he did what he did first, before the government comes forward and holds a press conference.

I was very aware that someone's life was on the line.

Did you have to live in Berlin to be able to finish this movie? Do you think you would have been able to finish it if you were still living in the U.S.?

I think there is a good chance that I would have gotten a knock on the door. I had a lot of footage. I was the first contact.

I've had my computer taken at the U.S. border. I've had agents tell me, 'If you don't answer our questions, we'll find our answers on your electronics.' It's pretty direct. Whether or not I could work … for me it wasn't worth testing.

What do you think the political response to the disclosures has been like? Has it met expectations or disappointed?

In general it's disappointing. The programs are still in place. I do think that there's sort of a shift in public consciousness not just in the U.S. but internationally. And there's been political pressure and there's also been commercial pressure, where you have companies saying, 'This is bad for business, guys, what are you doing to us?' You have Mark Zuckerberg going out and realizing this is a threat to their business.

In general I feel pretty disappointed. Even people who are our allies, like Wyden and Udall, they have immunity. If they want to release this information, which they've been saying the public has a right to know for all these years before Snowden unraveled his life, they could have done so with zero consequences, beyond perhaps losing a seat on a committee.

And of course the disclosures that you helped usher along caught James Clapper in that famous lie that Wyden provoked him into, that the NSA was not collecting information on millions of Americans.

Totally provoked him into.

Does that frustrate you? There's no clearer example of the limits of what the press can do, given that Clapper hasn't faced much in the way of political consequences.

It's frustrating. One of the most disturbing trends in the post-9/11 era is people who engage in illegality who are in the government are exposed to no repercussions. You have people who engaged in torture, or lie, perjure themselves or spy on Americans. All those kind of things, there is no response to them, and yet we go around chasing journalists or whistleblowers.

Do you follow the USA Freedom Act? Does any of that give you any hope?

Not a lot.

I do think probably the best or the most concrete shifts comes from increased privacy and the idea that encryption is a way to secure communications. And I think that tech companies are going to understand that customers will want that, and will provide it, and it will become easier for end-users to use encryption.

So Jacob Appelbaum's our only hope -- not Ron Wyden?

Yeah, I think so. The free software community, the people who are basically saying that crypto works and we're going to make it available to the public.

Going through all the documents from Snowden that you've read and all the stories that you've worked on, and given the fact that you were extremely privacy-minded before all this, what has surprised you the most about what the U.S. government is doing?

I guess the scale. The mentality of trying to collect as much of everything they can, and hold it for as long as they can, and be able to retroactively query it. I think the scale of it is one, and then the use of particular kinds of targeting.

I've done some reporting on how they've gone after engineers at telecoms. They've figured, OK, if we're interested in this network, we're going to go into it, we're going to find the engineer who is the keeper of the passwords, the system administrators, the engineers, and target them by their names in GCHQ documents. They go to their LinkedIn pages and give them a fake page that then infects their personal computer that then infects their network that they work for. That's pretty pernicious stuff.

You reveal in the film that Snowden's girlfriend has moved to Moscow to live with him. Given what Greenwald has said, what Snowden himself has said, about not wanting the disclosures to be about Snowden's personality, was it a difficult choice to include that in the film?

It was an easy choice. He doesn't want to be in the story and I understand that, but he did unravel his life to reveal these things and his motivations do matter. He manages to contact the press and get things into the world, and he also understands the really difficult personal consequences that's going to have for people he cares about, especially Lindsay. So I thought it was important. I didn't want it to be the end of the film, obviously. I felt the film is about his actions, not his fate.

You just mentioned his motivations. Some of the footage from Hong Kong was very humanizing. Was it tough to sit on some of that for 18 months while Snowden was continually getting beaten up and people were casting aspersions on his motivations?

I never really felt like I was sitting on it. It's longform. It's like writing a novel. It takes time. I wasn't just going on vacation. I've pretty much done nothing but work since Hong Kong. I hope to have a vacation one day.

I've been making films long enough, I want to make something that I know I'm going to be proud of in a year or two years or five years, not make something that's reactive to some media frenzy, which I was witnessing all around me. So I kind of bowed out of doing a lot of media. I didn't want to repeat the story a million times, because I knew that once I were to do that, my relationship to what happened would become alienated from what I needed in terms of the creative process.

Anyway, we finished it as fast as we could.

At the very end of the film, we're kind of introduced to a new character who's not shown at all. The second whistleblower, whoever it is. And to me it feels like a call for more whistleblowers. Is that what you meant it to be?

In terms of sources, I think it's wrong to count. I think there are multiple sources. Every journalist I know works with sources and there are many sources, so it's not about that. I think I was interested in -- Binney comes forward, and then you have Snowden. There are people who take these enormous risks and the risks are real.