In director Oliver Stone's new biopic, the actor portrays Snowden, who copied and leaked classified National Security Agency documents surrounding surveillance ethics in 2013, and he spent four hours with the computer expert while researching the role.

"A few months before we started shooting, I went to Moscow and I sat with him and (girlfriend) Lindsay Mills and we talked for about four hours," Joseph tells WENN. "It's funny because he's always trying to take attention off himself, personally, and put attention on the issues, but I'm an actor and obviously going to focus on him personally and want to get a sense of who he is as a guy.

"I watched how he sat, how he stood, how he shook my hand, how they eat their lunch. One of the first things I noticed was he actually has really good manners, which I found surprising. Nowadays, when you think of someone who is talented on computers you don't necessarily credit them with social graces.

"He's from North Carolina, where I think they put more emphasis on good manners than where I'm from in Southern California. He is sort of an old-fashioned gentleman. I wanted to incorporate that into the performance."

The Dark Knight Rises star also studied Snowden's voice, so he could sound a little like him, and the exiled techie was always available for star and director to make sure the story they were telling was accurate.

"There were a lot of great technical consultants on this movie, not to mention Snowden himself, who looked at several drafts of the script and gave feedback especially on the technical aspects. Making sure those lines sounded realistic to him," Joseph explains. "I had to really understand those words so that I wasn't saying gibberish."