The "Special" edition of the soundtrack includes a vast array of instrumental tracks (BGM) that build the drama's intense psychological atmosphere. Composed by artists like , Park Yoon-seo , and Lee Joon-wha , these pieces are often characterized by their eerie, discordant, or suspenseful arrangements.

: Tracks like "Inference," "Tracking," and "Evidence" use repetitive, driving rhythms to simulate the investigative process.

: A melancholic indie-rock piece that echoes the psychological isolation of the protagonist, Ryu Sung-joon.