Beginning in June 2000, it took Bong Joon Ho a year to write the script for Memories of Murder (2003), yet he has stated that: "For the first six months, I didn't write a line of the script. I just did research."
In order to make his character Detective Seo look properly worn-out by the stress of the case, actor Kim Sang-kyung deliberately limited his food intake and slept fewer hours.
One deleted scene shows detective Cho walking in a red light district, and then getting a massage from a girl as he asks her about possible leads regarding the murders. The scene was shot in a real red light district in the city of Jeonju and featured real sex workers. They had to ask the local pimp for permission to film.
Many viewers mistook Kwok Seol-yung as detective Park's wife and also thought that they were at their home in the scenes where they are together. She is actually a prostitute and they are at a brothel.
Bong Joon Ho has stated that the script for Memories of Murder (2003) was directly influenced by Alan Moore and Eddie Campbell's comic book From Hell, and that he was also "a bit disappointed with the Hughes brothers' film of it."