Based on Japanese mystery writer Keigo Higashino's 2005 novel "Yogisha X no Kenshin" ("The Devotion of Suspect X").
Early working Korean title was "Wonjeonhan Sarang" (literally "Perfect Love"), then changed to Yonguija X (literally "Suspect X").
Filming began December 10, 2011 and finished April 10, 2012. A party was held on April 10th at a restaurant in Nonhyeon-dong, Gangnam, Seoul to celebrate the completion of the movie. The party also celebrated lead actress Lee Yo-Won's birthday which was on April 9th.