Authors:

I did more research into the police procedure. I worked out with SWAT guys and ex- and active military guys, and consulted with them and read books. As far as the character itself, I don't know how you can research being a focused guy, aside from just being a focused person and knowing what that's like. Outside of the character background and all that, there wasn't a whole lot of other stuff to really delve into. You just do what you do.

Source: collider.com
I did more research into the police procedure. I worked out with SWAT guys and ex- and active military guys, and consulted with them and read books. As far as the character itself, I don't know how you can research