Ye-Jin Son and Soo Go did the nude scenes Themself without the use of a body double.
Actress Son Ye-jin was Park's first and only choice for the role of Yoo Mi-ho after having attended high school with her in Daegu. He said, "She was very quiet back then. I've seen her onscreen and thought she was very talented because she pulled off characters that were so different from how she was like in real life." Though Son was extremely flattered and called the project "her destiny," she didn't find the role easy because she was unaccustomed to playing a character so dark and sinister, and "wanted to make her look like someone deserving sympathy." For Son, the most difficult scene to film was the one in which her character appears nude and comforts her fiance's daughter after she is sexually assaulted by Yo-han. Son expressed her concern that the scene might be misinterpreted by audiences as vulgar or gratuitous, stressing that the scene is painful and a glimpse into Mi-ho's state of mind.
Director Park Shin-woo was inspired to write the script after being impressed with the novel Byakuyako. He sent the screenplay to author Keigo Higashino, who said it was "superb," and allowed it to be adapted into a film.
Park Shin-woo's feature directorial debut. He first drew attention after his short film About a Bad Boy won the jury award at the Mise-en-scène Short Film Festival.
The director then cast Han Suk-kyu as Han Dong-soo. The actor, then-44 years old, had initially turned down the role because he felt he was too young to play the 50-year-old detective. Han said, "I wished I would have been 10 years older, so I refused the part. But the director wrote me a handwritten letter explaining why he had to use me for the part... When I met him I was convinced by his sincerity, and I thought perhaps I wasn't challenging myself enough as an actor."