Justin Pendleton is one of two main antagonists in the 2002 film Murder by Numbers, the other being Richard Haywood.
He is portrayed by Michael Pitt, who also portrayed Mason Verger.
Pendleton is a rich and highly intelligent high school student and a close friend to Richard Haywood, another wealthy and intelligent student in his class. Together, they concoct a scheme to commit a "perfect murder" (by leaving no incriminating evidence) in order to show their superiority over everybody else. They drive around searching for a supposedly random target, and they decide on a specific woman whom they later kidnap and tie up. They then murder her and set up the school janitor Ray Feathers (who sells Haywood marijuana).
Detective Cassie Mayweather takes on the case and finds clues that make her suspicious of Pendleton and Haywood. She questions them both at their school, and Pendleton claims that he doesn't socialize with Haywood and they have nothing in common. Pendleton becomes romantically involved with a girl in his class named Lisa Mills, but when Haywood sees them kissing, he becomes jealous and sends Pendleton a video of him and Lisa making love. Pendleton becomes angry but Haywood claims he did it for his own good, to show him that Lisa is "easy" and isn't good enough for him. Meanwhile, Cassie becomes determined to prove that they are both guilty and slyly takes photographs of them together (despite Pendleton telling Haywood that they shouldn't be seen together in public). Cassie and her partner Detective Sam Kennedy later bring both Pendleton and Haywood in for questioning, and Cassie believes that Haywood was the actual murderer and Pendleton was merely his accomplice. She tries to convince him to speak by telling him that since he wasn't the actual killer, he will be let off if he talks - however, neither Pendleton nor Haywood reveal any information and they are therefore released.
After Haywood tries to save himself by making a false "confession" to the DA, Cassie immediately tries to have them both arrested. Pendleton finds Lisa and tells her the truth about the murder before fleeing to his and Haywood's remote resort where they killed their victim. Lisa phones the police and tells them where to find Pendleton and Haywood, just as Pendleton and Haywood prepare to commit suicide. Pendleton realizes that Haywood's gun is empty, and that he planned to watch Pendleton kill himself alone. At that moment, Cassie enters and Pendleton surrenders, but Haywood shoots at her and accidentally injures Pendleton instead. Cassie pursues Haywood out onto the balcony and sends him falling to his death, but the balcony begins to break and Cassie is left hanging onto the edge. She pleads with Pendleton to save her, which he eventually does, and she tells him that he will likely get a light sentence as a result. However, when Cassie examines the strangulation marks on the dead woman's neck, she realizes that Haywood was not the one who strangled her - it was in fact Pendleton. Cassie and Sam then trick Pendleton into confessing, though he pleads with her to let him go since he saved her life. Cassie reminds him that people only get one chance at life, and they must therefore live with the consequences of how they choose to live it. A grief-stricken Pendleton is then arrested and presumably executed.