If you are going to roleplay correctly, please keep your feelings to yourself. Just because someone killed your character does not mean you can recreate and pretend like you are someone who seen the murder happen.
Note: I am not going to sit around for you to get my character killed by a mass group of people, because you felt like newbie killing and things did not turn out your way.
HELP: Is there any way I can report such actions before it is too late?
Email the mud with this kind of thing.
Yeah, definitely e-mail the MUD, don't post it here (assuming this is an actual incident). If its serious/urgent, wish up.
In my opinion, if you are concerned that a situation is being ooc motivated by the murder of a prior pc, you should first wish up and state, :
'This player <insert name or sdesc> is behaving in a manner that makes me suspect it is a PC I murdered a few days ago <insert dead pc's name and/or sdesc>. If someone could see if this is the case I would really appreciate it."
It is a straight-forward wish, gives the imms all of the pertinent information they would need to look into it, and if they respond with a simple 'will look into it' then your part of the situation is over with. It would be in their hands at that point to determine the legitimacy of the behavior. If they find the two pc's linked by the same account or login domain they would likely deal with the character directly, and if they find no such link you should assume the silence to represent the situation being kosher.
If you don't get a response when you wish up, then yeah, simply email a similar query to the mud. From personal impression the imms will jump on an ooc abuser like a heroine addict grabbing for a loaded needle. (and rightfully so since it betrays so much of what the IC environment represents)
Ok, I mailed the mud.
I'm going to wait for my response, and see what happens after that.
Definitely email the mud, but dont expect a response. The mud gets spammed with hundreds of emails per day. It is however safe to assume the matter will be looked into, even if you dont hear back.