When the most important decisions are made in secret, we lose our ability to check the powers that control.

In all my work, I'm interested in trying to understand the human consequences of government policies.

I was in correspondence with an anonymous source for about five months and in the process of developing a dialogue you build ideas, of course, about who that person might be. My idea was that he was in his late forties, early fifties. I figured he must be Internet generation because he was super tech-savvy, but I thought that, given the level of access and information he was able to discuss, he had to be older.

We're definitely in an era where the government wants to keep more secrets and it wants to come after anyone who's exposing those secrets and in many cases exposing government illegality. They're coming after the journalists and they're coming after the whistleblowers. It's not a good sign if the government is expending much energy trying to find out who journalists are talking to.

In terms of sources coming forward, I really reject this idea of talking about one, two, three sources. There are many sources that have informed the reporting we've done and I think that Americans owe them a debt of gratitude for taking the risk they do.

I think one of the most shocking things is how little our elected officials knew about what the NSA was doing. Congress is learning from the reporting and that's staggering. Snowden and [former NSA employee] William Binney, who's also in the film as a whistleblower from a different generation, are technical people who understand the dangers.

It's not everyday that a whistleblower is actually willing to be identified.