Amy Ryan looked and sounded so convincing as a working-class Dorchester mom that a security guard mistook her for a fan on the first day of location filming and wouldn't let her on the set. One of the producers finally noticed her on the other side of one of the barricades and said she should be let through. The incident made Ryan twenty minutes late, but convinced her the Boston accent she'd prepared was realistic.
The film's UK release, scheduled for December 28, 2007, was postponed for almost six months, because of the film's similarity to the real-life case of four-year-old Madeleine McCann, who disappeared from the holiday apartment where she and her family were staying in Praia da Luz, Portugal, on May 3, 2007.
Jill Quigg was discovered when the production's barricades in the streets of Boston prevented her from picking up her son from school. Ben Affleck was so impressed by her loud rants against the film crew that he asked her to read for the movie.
On the DVD commentary, Ben Affleck says that he and Jill Quigg improvised the scene early in the movie in which Quigg (as Dottie) talks to the press about the flyers they had posted and the vigils they had planned. Affleck says that he would feed her some lines and then she would perform them. Her mispronunciation of the word "vigil" as "visual" came from her mishearing what Affleck had said from behind the camera, but he later decided to keep it the way she had said it.
Amy Ryan was so convincing with her Boston accent in her audition that writer and director Ben Affleck asked her what part of Boston she was from.