Yamens are guardians of justice.
Every single PKer (player killer) is listed in their wanted list.
In early WOKF they was not only NPC. But when some GMs left, Yamen players dissapeared forever now anti-pk schools helps to keep justice in game.
Yamen NPC is very useful source of information about PKers.
Player Killer is player who attacks and kills other players. They have colored names in 4 different colours
That depends on their PK points. Yellow names are not PKers yet but they attacked someone (they have no PK points).
If you'll get even 1 PK point (orange name) you are listed on criminal list in Yamen. There, everyone can know, where are you, who are you, what lvl are you, what class and what school are you in. It's very useful for Anti-PK schools that hunt PKers, like Yamen players did before. They also shows how many PK points you already have, and how many players you killed.
Yamens of course gives a way for criminals to pay back their crimes. You need to pay money to them to make you less wanted.