I’m so sorry about your nephew.
It would be a good thing if we could recognize the origins of harmful behaviors in order to prevent their occurrence (sp?) I’ve seen families of six children, four of whom were fine, upstanding citizens, and two of whom were hopeless reprobates. It’s not all nurture, but some if not all nature plays a part.
Kid had great nurture and a brother who turned out fine. It’s just bad seed. One thing every monster has in common is they at least had parents and probably siblings.