There is a social compactcontract that exists for dnd,D&D - it sounds like one of your players is breaking it.
The compactcontract is basically we are all nerds, let's get along. Be nice to one another.: we are all nerds, let's get along. Be nice to one another.
There is no problem with a pcPC murdering another pcPC, so long as it is part of the game (you killed my father! The bounty on your hwad was to high for me to resistYou killed my father! The bounty on your head was too high for me to resist.). PvpPvP is generally only okOK in an evil group, andand only if all of the players involved are OK with it.
The problem here is one of your players does not like another player, andand is bullying them.
Get rid of the bully, explain to them the social contactcontract of dndD&D. Tell them what you think they are doing (bullying). Let than obitsthem know that it is socially unacceptable, andand they can either stop it or stop coming.