Because of internal problems with the film's original distributor, First Look International, the film was not released theatrically. The Showtime television network officially premiered An American Crime on May 10, 2008.
The film was nominated for a Golden Globe, a Primetime Emmy (both for Keener's performance), and a Writers Guild of America Award.
Sixteen-year-old Sylvia Likens (Ellen Page) and her 15-year-old sister, Jenny (Hayley McFarland), have, in the past, travelled with their parents who work on the carnival circuit. She and Jenny now live with their mother, Betty Likens (Romy Rosemont), who recently separated from their father, Lester Likens (Nick Searcy). Betty reconciles with him, and they decide to go on tour together. They agree to leave their daughters in the care of a single mother named Gertrude Baniszewski (Catherine Keener), whose daughters the Likens girls met in church. In dire financial straits, Gertrude offers to care for their daughters for twenty dollars a week, and as their parents leave, the girls settle in with Baniszewski's six children: Paula (17), Stephanie (16), Johnny (13), Marie (12), Shirley (10), and infant son Kenny. Sylvia befriends Paula (Ari Graynor), who confesses to Sylvia that she is pregnant by her married boyfriend—Sylvia swears not to tell. Soon after the girls' arrival, Gertrude is upset that Lester's weekly payment is late and punishes the girls by whipping them with a belt. The payment, along with a letter from the parents, arrives shortly thereafter, but Gertrude throws the letter in the trash and says nothing to the Likens girls.
While Paula and Sylvia are out with friends, Paula's boyfriend tells her that he can no longer see her, then hits Paula when she pleads for him to stay with her. To stop the boyfriend's attack, Sylvia tells him that Paula is pregnant. Paula, furious, vows that Sylvia will pay for revealing her secret. Ricky Hobbs (Evan Peters), a neighbor of the Baniszewskis, who is attracted to Sylvia, observes the scene. Paula tearfully tells Gertrude that Sylvia has been spreading lies about her. Gertrude forces Sylvia to apologize, and has her son Johnny (Tristan Jarred) hold Sylvia so that Paula can beat her. Rumors spread around their school that Paula is pregnant. Jenny finds the letter from her parents in the garbage, prompting Sylvia to phone them. The call is cut short when they see the Baniszewski children, who tell their mother about it. Although the girls had traded bottles in for money to make the call, Gertrude believes they stole the money from her and burns Sylvia's hand with a cigarette for "stealing".
At a church lunch, Andy (James Franco), the father of Gertrude's infant son, tells her that Sylvia has been spreading rumors that Paula is pregnant. When Sylvia returns home, Gertrude accuses her of flirting with Andy at the lunch and telling more lies about her daughter. Intending to make an example of her to her children, Gertrude forces Sylvia to insert a Coke bottle into her vagina in front of them. Gertrude then orders Johnny and Stephanie's boyfriend, Coy Hubbard (Jeremy Sumpter), to throw her down the basement stairs, and lock her in. When Jenny asks how long Sylvia will be down there, Gertrude replies "until she learns her lesson," then tells everyone to maintain the fiction that Sylvia was sent to a juvenile detention facility.
Johnny begins to bring neighborhood children into the basement so they can join in the ongoing torture and humiliation of Sylvia begun by Gertrude and her children, assuring them that his mother said it was all right. The children regularly visit, with Gertrude's knowledge and approval, to beat Sylvia and burn her with cigarettes. Paula, feeling guilty, tells her mother she has been praying and thinks Sylvia has been punished enough, but Gertrude ignores her pleas. Their pastor visits the Baniszewski home, informing Gertrude that Paula told him she was pregnant and hinted to him about Sylvia's abuse. Gertrude reassures him that Sylvia was sent away for being a bad influence, and as the pastor leaves, she orders everyone into the basement. Straddling Sylvia on the basement floor, Gertrude begins to carve the words "I'M A PROSTITUTE AND PROUD OF IT!" on Sylvia's abdomen with a hot needle, but is unable to continue and orders Ricky to finish the branding.
Late one night, Paula helps Sylvia escape by carrying her up the basement stairs and out of the house. Awakened by one of the Baniszewski girls, Gertrude tries to prevent the escape, but Paula stops her. Ricky finds Sylvia and drives her to her parents, who are horrified at their daughter's condition. Sylvia and her parents go immediately to the Baniszewski household to make sure that Jenny is safe. Sylvia walks into the house and sees her own lifeless body lying on the floor with Stephanie leaning over it screaming that she is not breathing. As she stands to watch this, Sylvia closes her eyes and vanishes, revealing her escape and return to be only a hallucination just before dying. While Gertrude continues to insist that Sylvia is faking, Ricky calls the police. As they arrive, Jenny approaches one of the officers, saying "Get me out of here and I'll tell you everything."
On the witness stand, Jenny tells the prosecutor that Sylvia never did anything to Gertrude, Paula, or anyone else, and adds that Gertrude had threatened her with the same treatment her sister received if she did not keep quiet about it. After denying that she did anything wrong, and blaming the torture and death of Sylvia on her children and their friends, Gertrude is found guilty of first-degree murder and sentenced to life in prison, leaving her children to cry over losing their mother to the law. As Sylvia's narration details the punishment of some of her abusers, Gertrude sits alone in her prison cell. In her imagination, she sees a vision of Sylvia silently looking back at her. Gertrude tries to speak but is unable to get the words out, and the image vanishes. The spirit of Sylvia is then shown at the circus, riding the merry-go-round, expressing that it is the only place she has ever felt safe.
Principal photography took place in 2006. Most of the cast were completely unaware of the real Likens murder until after they read the script, which was based largely on actual court transcripts from the case. Catherine Keener originally turned down the role of Gertrude Baniszewski; however, after she could not get the story out of her head, she met with director Tommy O'Haver and agreed to do the film. Ellen Page was the only choice to play Sylvia Likens.
The film received generally mixed reviews. On Rotten Tomatoes, the film has a rating of 23%, based on 13 reviews, with an average rating of 4/10. Ginia Bellafante of The New York Times called the film, "...one of the best television movies to appear in years" and praised Catherine Keener's portrayal of Gertrude Baniszewski.