I want to make sure everything has my 100%.

I read as many books about the psychology of a psychopath as I could and I researched what exactly happens to soldiers.

You get a role like this in a big action movie [like Jack Reacher] and you can go one of two ways: you can paint in broad strokes, which happens a lot in action films, or you can get very detailed.

Psychopaths don't have that charming skill set. They definitely manipulate, but they do it through focused, unskilled means. They're more obsessive.

The role I played [in theatre] was originated by Ian McKellen in 1979 and he came. I didn't know he was there and I walked out at the end of the play, which is a very intense play - my character is required to do some really horrible things - and the director was waiting backstage and he goes, "Obviously I didn't want to tell you guys, but Ian was here today" and we, of course, freaked out.Ian McKellen said some really beautiful, kind things, one of which was, "It's so much harder to watch than it is to do."

A sociopath can imitate emotions, where a psychopath really doesn't have that capacity. They can't fool people into thinking anything and they're usually lacking major empathy for anybody besides themselves.

I change myself a lot. Some roles you don't want to be big, bulky, muscle-y guy and some roles you want to be a lean, marathon-runner physical type. And some roles you just don't want to be in shape.