Suspect X is a 2008 Japanese crime thriller film directed by Hiroshi Nishitani, based on the novel "The Devotion of Suspect X" by Keigo Higashino. The story revolves around a well-known mathematics teacher Tetsuya Ishigami, who helps his neighbor Yasuko Hanaoka to cover up a murder she committed in self-defense against her abusive ex-husband. However, when the body is discovered, Detective Kaoru Utsumi is assigned to investigate the case and she quickly suspects Yasuko.
Despite the lack of evidence, Tetsuya Ishigami's behavior becomes increasingly suspicious and Detective Utsumi realizes that he might be involved in the case. However, Tetsuya has a brilliant mind and uses his knowledge of mathematics to create a perfect alibi for Yasuko, making it nearly impossible for the police to prove her guilt.
As Detective Utsumi delves deeper into the case, she starts to uncover Tetsuya's motive for helping Yasuko and realizes that he is far more dangerous than she initially thought. The film builds up to a tense and surprising finale as the truth is finally revealed.
Suspect X is a well-crafted thriller with a complex plot and intriguing characters. The performances by the cast, especially Masaharu Fukuyama as Tetsuya Ishigami, are excellent, and the direction by Hiroshi Nishitani keeps the audience engaged throughout. The film was a commercial success in Japan and has been highly acclaimed by critics and audiences alike.