Steve Niles originally conceived the story as a film. After years of rejection by studios, it was reworked into a comic book. Eventually, a studio that rejected the original screenplay went for the comic version.
According to the DVD commentary, Josh Hartnett was sick with mono for two weeks of filming. During that period, he had to fly to Venice, London, New York, and Los Angeles for premiers of The Black Dahlia.
The trivia items below may give away important plot points.
The Stranger and the grandmother were killed in the original script. The scenes where Eben and Stella find The Stranger in the station, and when Marlow comes back to him, were written during production and squeezed into the shooting schedule with the understanding that they would probably not be used.