1x1 - Unforgivable

Yifan joins SOD successfully. His first case is a serial killing where the perpetrator has the habit of stealing the victim’s shoelace as his trophy. This modus operandi leads SOD to believe that it is connected to a sexual crime committed 10 years ago. As they try to search for clues from both cases, the perp kills again. This time, he did not wait for 10 years.