Not a kill per say but I ultimately caused his death. So was looting a town and i met another player didnt kill me at first so I was thinking yay! So we stayed close to each other for a bit until zeds separated us. We meet each other again in cherno and he tries to kill me with his crowbar so i shoot him in the legs with my double barrel and bookd it. Well he follows me and still tries to kill me so I did the next most sensible thing piss off as many zombies as humanly possible and transfer the aggro over to him.