Look people, whether someone stole a kill from you or not it never justifies you kill stealing. Doing that puts BOTH of you in the wrong because you are BOTH abusing a bug. If you truly want a kill stealer stopped, firstly make sure they really are kill stealing and try talking to them. It could just be a misunderstanding,. If they are kill stealing, make a petition for a GM and record the conversation of the offending player using a command (Can\'t remember what it is, it\'s in the help button).
Really, the best thing you can do is let a GM know and walk away.