There are people who are always going to try to engage in activity that is illegal and they're going to try to subvert surveillance. But everybody should not give up their liberties and rights to privacy because some people are going to [do that]. We shouldn't stop or limit our basic liberties because some people are going to engage in criminal activities.

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 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.

Just consider the CIA and its effort to suppress the Senate's review of its torture program. Take in the fact that we live in a country that a) legalized torture and b) where no one was ever held to account for it, and now the government's internal look at what happened is being suppressed by the CIA. That's a frightening landscape to be in.

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.

I don't speak Arabic - I know a little to get by, but that's all.

In all my work, I'm interested in understanding big issues through the lives of individuals.