The Devotion of Suspect X is a critically acclaimed 2005 Japanese mystery novel by Keigo Higashino, the first in the Detective Galileo series, about a brilliant mathematician who orchestrates a perfect alibi for his neighbor, a single mother who killed her abusive ex-husband, leading to a battle of wits with a physicist detective. The novel subverts the typical whodunit by revealing the crime early, focusing instead on the intellectual puzzle of how the cover-up was achieved and the psychological motivations behind the characters' actions.
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For those wondering.
https://en.wikipedia.org/wiki/The_Devotion_of_Suspect_X