Can't set people unessential

[RichterQ87]

So I recently decided to make a serial killer character in Skyrim and to rid Skyrim of all annoying and asshole people to make it a better place. So naturally, I started with Heimskr, worked fine, no issues. But then my next order of list was of course, Nazeem. But when I tried to kill him, it turns out, he´s suddenly essential? I can't kill him no matter what I do. Not even with sneak tools. I've tried attacking him normally, just gets downed, I tried killing him with an arrow, just gets downed and I've even tried killing him in his sleep with sneak tools but nothing happened. So after about 2 hours of trying to kill him, I decided to leave him for a while and move on to another target in Markarth, Ynvar the Singer since the first time you see him he'll say "Outsiders, pfft". However, when I try and kill him, he just gets fucking downed. I've tried setting them unessential via console with

"Setessential "His id" 0" and the console shows no error but when testing it, he still won't die. 

My first instinct was some mod conflicting with sneak tools or some old mod that I've uninstalled and left a lot of NPC's essential but when I checked the nexus page of sneak tools, it says nothing about any mod conflicts. So that leaves me with, what mod could possibly be ruining my experience? Does anyone have an idea?

 

Any help would be deeply appreciated so I can go back to ridding Skyrim of assholes