dacnomaniac

A person that's obsessed with murder/killing.

Dacnomania - obsession for murder/killing

I think John is a dacnomaniac, because he is obsessed with killing

Dacnomaniac

The unhealty obsession, desire, or compulsion of killing

Dude! that guy has a life sentence for 30 counts of 1st degree murder on the species - Eg, and assault on their leader - Lord Eg! He must be a Dacnomaniac