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.

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

The fact that the CIA knew that two of the 9/11 hijackers were entering the United States and didn't notify the FBI and that nobody lost their job is shocking. Instead, we occupied Iraq, which had nothing to do with 9/11. I mean, how did those choices get made?

One of the things that I think is true is that encryption actually is able to secure our communications, that every individual can use encryption, and that it's accessible and in many cases free.

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.

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

One of the most frightening things, I think, is the capacity for retroactive searching, so you can go back in time and trace who someone is in contact with and where they've been.