The world of Thain is not a static place, and often NPC's will respond to on-going RP. This includes the killing of guards and commoners and failed pick-pocket attempts, which can result in other guards etc. coming after you. Although single incidents can be "forgiven" after a server restart, a serial killing spree may well end up with the guards "remembering" you over restarts. Also guards, and perhaps even other players will often react to monstrous looking things - these include polymorphed/shifted forms and characters sprouting wings/horns/tails and such like.
Please also see entry on permission to play monstrous characters here.