The series is based on the 2018 non-fiction essay book of the same title, co-written by Kwon Il-yong, South Korea's first criminal profiler, and journalist-turned-author Ko Na-mu, drawing on Kwon's real field experiences.

The drama recreates the late 1990s, a period when motiveless murders surged in South Korea, using only the dramatic elements drawn from the source book to build a nonfiction crime psychology drama.

Producer Park Young-soo explained that because the story is based on the real case of Kwon Il-yong, who established criminal profiling techniques in South Korea and helped them gain worldwide recognition, the production centered its story around the Criminal Behavior Analysis team at the Seoul Metropolitan Police Agency's Scientific Investigation division.

Kim Won-hae and Kim Nam-gil were cast together again three years after previously working together on the SBS drama Yong-pal (Diabolical), formally titled Life on the Line in Korean, actually referenced as 'Hot Blooded Priest' (Diabolic Priest) in the source.

Producers deliberately cast well-established actors in their 40s, such as Jin Seon-kyu and Kim Nam-gil, in the lead roles rather than typical younger stars.

The show was originally slated to follow the drama 'Hong Chun-gi' as a Monday-Tuesday series, but was ultimately confirmed as a 12-episode Friday-Saturday drama instead, partly due to scheduling considerations tied to the pre-produced drama 'Our Beloved Summer' and its overseas licensing review.

Due to the graphic and dangerous nature of its subject matter depicting increasingly brutal crimes, South Korea's Ministry of Gender Equality and Family officially designated the series as harmful media content for youth under the Youth Protection Act.

The show was broadcast during a competitive period as SBS aimed to secure strong ratings against rival networks' Friday-Saturday dramas, leading to its premiere date being finalized for January 14, 2022.