Each case is related to something special. Every trace breaks off somewhere without giving the detectives any logical solution. Everyone is different and understands the concept of serial killing differently. Some only catch evidence, others are intuitive and accurate. There is one case and there are countless detectives. What will each of them have to go through to get to the very end of the serial murder path? Will any of them find a solution?

Because it's an exception, hence the preference.

Original +bonus on Wattpad @lux1228

Everything is wrong... all wrong! The letter wasn't written by Tang Xueying...