As Saoirse Ronan matures over the years, so do her roles. Since playing the part of Briony Tallis in Atonement, Ronan chose a darker, more mature role of a slain teenage girl in her upcoming movie, The Lovely Bones.

Directed by Peter Jackson and based on Alice Sebold’s best-selling novel of the same name, the film features Ronan as Susie Salmon, a young girl who is killed and then watches over her family from heaven. The Lovely Bones’ screenplay, written by Jackson, Fran Walsh and Philippa Boyens, does not incorporate some of the darker elements originally integrated into the novel, including more violent and graphic imagery and a rape scene. However, Ronan said the exclusion will not take away from the story.

“I think, if anything, it makes it stronger because it’s the easy route to put that kind of scene in,” Ronan said. “It can make people uncomfortable. It can make people too disturbed. And I find that if they do it the way that we did in The Lovely Bones, which was a very tasteful way to do it, I think it just leaves it up to the audiences’ imagination, and sometimes that can even be stronger.”

Ronan said although she related to Susie’s character, preparing for the darker aspects of the role was a challenge. She communicated with Jackson throughout filming, continuously working to put herself in the right mindset in order to portray the role of the murdered girl accurately.

“It was challenging,” Ronan said. “It’s a very serious subject matter, and it was always going to be a challenge for me because I hadn’t done anything quite that deep before. When we dealt with very emotional scenes — intense scenes — there would be a lot of discussion between me and Pete, Fran and Philippa. We just talked a lot about it and made sure that we were on the same page.”

Ronan said she waited to read Sebold’s novel until after production and filming in order to focus on the screenplay’s interpretation.

“I just really wanted to focus on the screenplay version,” Ronan said. “I read the book this year for the first time, and I absolutely loved it. I felt every emotion possible. And I think because I had been through the whole experience of making the movie and living through the story, I think that helps me to really connect with the book and to understand the book fully.”

After the release of the Academy Award-winning Lord of the Rings trilogy, Jackson has continued to produce visually groundbreaking films. The Lovely Bones is no exception, according to Ronan, who said she was pleased with the post-production results of the blue-screen-produced heaven scenes.

“It was great,” Ronan said. “I saw the movie a few days ago, and it was a lovely surprise to finally see heaven. I think their plans for heaven seemed to work really well.”

Despite the elements of murder, revenge and justice, Ronan said the movie conveys an uplifting message of hope.

The Lovely Bones hits theaters Dec. 11 and also stars Mark Wahlberg, Rachel Weisz and Susan Sarandon.