When Peter Sarsgaard was cast in the third season of AMC's The Killing, fan reaction was nearly unanimous: He's perfect. The crime drama's world is dark, murky, complex, and amoral all adjectives that also describe Sarsgaard's turns in films like Jarhead and Boys Don't Cry. The 42-year-old actor admits his age factored into his decision to pursue TV. ''I feel like a lot of movies these days are shot for an audience younger than me,'' he says. But it was also the great challenge the Killing role posed: The lion's share of his scenes take place in a solitary prison cell, owing to the fact that Sarsgaard plays monstrous death-row inmate Ray Seward, a murderer from the past of former detective Sarah Linden (Mireille Enos). The constraints and the task of making scenes in the same setting interesting enticed him. ''I like restrictions,'' Sarsgaard says. ''The more restrictions the better. It's a challenge because it is difficult to keep [''introducing''] variety in a confined space.'' Space aside, Sarsgaard's ultimate goal was to make his killer as frightening as possible while still making fans sympathize with him. ''The big philosophical issues he's dealing with are ones we all wrestle with,'' he says, ''like forgiveness.''