Player-Killing (PK) on DartMUD is basically unrestricted. If you can manage to successfully kill (or otherwise harm) a character, you may do so.
Also note that DartMUD has permadeath: your character may die completely and permanently.
If you cannot stand suddenly losing a character that you have worked for months or years to build, be it at the hands of another player character or even by accident, DartMUD may not be for you.
Actions have consequences. Sulamar, the God of Fate, has been known to take an active interest in the fates of those mortals who seem to take an active interest in the fates of their peers.
Avoid killing people just for fun. It's not good for the game, and you will be dis-invited to play. See 'help lameness'.
That being said, for the most part, the creators generally make it a point not to care who is killing who and for what reason.
If someone kills you, and you think that it was because of a dispute you had with their previous character two years ago, or because you hate each other IRL, or really for any reason at all, it may very well be a bogus reason, but we really don't care.
We don't, can't, and shouldn't have to keep track of all that. It's impossible to prove, and we are not going to waste our time thinking about it.
If someone manages to kill you without multiplaying, multicharing, botting, abusing a bug, or using OOC communications, you are dead, pure and simple.
If someone does break the rules in the process of killing you, we will assuredly punish them, but we are not obligated to restore you, or even to discuss it with you. If you do get restored, it's because we are being unusually nice. Count your lucky stars.
An armed society is a polite society. Your best bet: be nice to others, be careful, and watch your back.