As an actress, Elizabeth Banks is impossible to put in a box. In one fall movie season, she was alternately in a comedy about a homemade porno at the same time she appeared in “W.” as former first lady Laura Bush. Even now, while starring as Jack Donaghy’s love interest in NBC’s comedy “30 Rock,” she’s appearing in theaters as a suicidal heroine in the suspense film “The Next Three Days,” alongside Russell Crowe.

“I feel like I was getting a little bit caught up in being the girl in a bunch of boy’s funny movies and it just becomes less interesting the more and more you do that,” the actress explains while munching on some M&M’s at the Waldorf Astoria Hotel. “To be presented with something that was going to challenge a whole other set of tools that I have as an actor ... it was such a no-brainer.”

In the “The Next Three Days,” her character Lara Brennan is accused of a murder that she claims she didn’t commit. As it becomes clear that she cannot escape her fate behind bars and her mental health begins to deteriorate, husband John (Crowe) plans to go to any lengths to save her.

In order to understand the monotony of doing time in prison, Banks interviewed nonviolent inmates to learn the details of their day-to-day lives.

“There are all these little battles that they’re fighting every day in there, to have a sense of their humanity and their old life,” she says.

Perhaps because of this research, the role of a woman on edge behind bars manages to avoid cliche in her hands.

“We didn’t want Lara Brown to be this sour, woe-is-me woman in prison,” Banks explains. “It was all about bringing a sense of light in her so that you believed that Russell needed her in his life. I think the audience goes on the ride of this movie because they believe that this couple is great together.”